Add splitted sorted array search
En Yi
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6b23f5cdfa
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/**This is the code for search an index in a splitted sorted array
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Thought it was interesting.
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If there are duplicate elements, it is not guarantee that the index return
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is the smallest index.**/
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#include <iostream>
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#include <stdlib.h>
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#include <time.h>
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#include <algorithm>
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int generate_random_number(int upper_bound);
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void print_array(int array[], int n);
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int binary_search(int array[], int lo, int hi, int val);
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int splitted_array_search(int split_array[], int lo, int hi, int val, int n);
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int main(int argc, char** argv){
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int n;
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int upper_bound;
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// Input checking. Could've used a loop, but I'm not bothered :p
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if(argc == 3){
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char* endp;
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char* endp2;
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int val = strtol(argv[1], &endp, 10);
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int val2 = strtol(argv[2], &endp2, 10);
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if (!*endp && !*endp2){
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n = val;
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upper_bound = val2;
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}else{
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std::cout << "Usage: ./split_array val1 val2"<< std::endl;
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std::cout << "val1 is the length of the array, int" << std::endl;
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std::cout << "val2 is the upper bound of the random number (exclusive), int" << std::endl;
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return 1;
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}
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}else{
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std::cout << "Usage: ./split_array val1 val2"<< std::endl;
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std::cout << "val1 is the length of the array, int" << std::endl;
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std::cout << "val2 is the upper bound of the random number (exclusive), int" << std::endl;
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return 1;
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}
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// Randomisation
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srand (time(NULL));
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int array[n];
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for(int i=0;i<n;++i){
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array[i] = generate_random_number(upper_bound);
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}
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// Sort it
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std::sort(array, array+n);
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std::cout << "Original" << std::endl;
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print_array(array, n);
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// Split array, put as a separate array
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int split_ind = generate_random_number(n);
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std::cout << "Split point: " << array[split_ind] << std::endl;
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int split_array[n];
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for(int i=0;i<n-split_ind;++i){
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split_array[i] = array[split_ind+i];
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}
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for(int i=0;i<split_ind;++i){
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split_array[n-split_ind+i] = array[i];
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}
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std::cout << "After" << std::endl;
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print_array(split_array, n);
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int val;
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if (generate_random_number(2) == 1)
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val = generate_random_number(upper_bound);
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else
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val = array[generate_random_number(n)];
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std::cout << "Finding " << val << "..."<<std::endl;
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int pos = splitted_array_search(split_array, 0, n-1, val, n);
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if (val >=0)
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std::cout << val << " is at index " << pos << std::endl;
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else
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std::cout << "Value not found" << std::endl;
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}
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int generate_random_number(int upper_bound){
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return rand() % upper_bound;
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}
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void print_array(int array[], int n){
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for(int i=0;i<n;++i){
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std::cout << array[i] << " ";
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}
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std::cout<<std::endl;
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}
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int splitted_array_search(int split_array[], int lo, int hi, int val, int n){
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if(hi<lo)
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return -1;
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// Binary search if the values of hi > lo as the range specified is sorted
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if( split_array[lo] < split_array[hi])
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return binary_search(split_array, lo, hi, val);
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//std::cout << lo << " " << hi << std::endl;
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int mid = (lo+hi)/2;
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// Get lucky
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if (split_array[mid] == val)
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return mid;
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// Check which side the the mid and query val are at
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// false for left, true for right
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// This is exploiting the fact that the right side is smaller than the left
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bool mid_side, val_side;
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mid_side = split_array[mid] < split_array[0];
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val_side = val < split_array[0];
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// Recurse search, but reduce the range accordingly
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if(mid_side == val_side){
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if (split_array[mid]<val)
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return splitted_array_search(split_array, mid+1, hi, val, n);
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else
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return splitted_array_search(split_array, lo, mid-1, val, n);
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}else{
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if(mid_side)
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return splitted_array_search(split_array, lo, mid-1, val, n);
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else
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return splitted_array_search(split_array, mid+1, hi, val, n);
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}
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}
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int binary_search(int array[], int lo, int hi, int val){
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// Just a normal binary search
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//std::cout << "Binary Searching..."<< std::endl;
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while(lo <= hi){
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//std::cout << lo << " " << hi << std::endl;
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int mid = (lo+hi)/2;
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if (array[mid] == val)
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return mid;
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if (array[mid]>val)
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hi = mid-1;
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else
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lo = mid+1;
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}
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return -1;
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}
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@ -0,0 +1,167 @@
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/** This is a command line visualiser of the search
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Please use a small number of array for this, otherwise it will break the printing.
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This is not guarantee to work on all OS. Works on linux.**/
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#include <iostream>
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#include <stdlib.h>
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#include <time.h>
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#include <algorithm>
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#include <unistd.h>
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int generate_random_number(int upper_bound);
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void print_array(int array[], int n);
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int binary_search(int array[], int lo, int hi, int val, int n);
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int splitted_array_search(int split_array[], int lo, int hi, int val, int n);
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void print_search(int split_array[], int lo, int hi, int current, int n);
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int main(int argc, char** argv){
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int n;
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int upper_bound;
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// Input checking. Could've used a loop, but I'm not bothered :p
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if(argc == 3){
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char* endp;
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char* endp2;
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int val = strtol(argv[1], &endp, 10);
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int val2 = strtol(argv[2], &endp2, 10);
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if (!*endp && !*endp2){
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n = val;
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upper_bound = val2;
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}else{
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std::cout << "Usage: ./split_array val1 val2"<< std::endl;
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std::cout << "val1 is the length of the array, int" << std::endl;
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std::cout << "val2 is the upper bound of the random number (exclusive), int" << std::endl;
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return 1;
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}
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}else{
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std::cout << "Usage: ./split_array val1 val2"<< std::endl;
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std::cout << "val1 is the length of the array, int" << std::endl;
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std::cout << "val2 is the upper bound of the random number (exclusive), int" << std::endl;
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return 1;
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}
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// Randomisation
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srand (time(NULL));
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int array[n];
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for(int i=0;i<n;++i){
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array[i] = generate_random_number(upper_bound);
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}
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// Sort it
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std::sort(array, array+n);
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std::cout << "Original" << std::endl;
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print_array(array, n);
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// Split array, put as a separate array
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int split_ind = generate_random_number(n);
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std::cout << "Split point: " << array[split_ind] << std::endl;
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int split_array[n];
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for(int i=0;i<n-split_ind;++i){
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split_array[i] = array[split_ind+i];
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}
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for(int i=0;i<split_ind;++i){
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split_array[n-split_ind+i] = array[i];
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}
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std::cout << "After" << std::endl;
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print_array(split_array, n);
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int val;
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if (generate_random_number(2) == 1)
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val = generate_random_number(upper_bound);
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else
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val = array[generate_random_number(n)];
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std::cout << "Finding " << val << "..."<<std::endl;
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usleep(1000000);
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int pos = splitted_array_search(split_array, 0, n-1, val, n);
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std::cout << std::endl;
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if (val >=0)
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std::cout << val << " is at index " << pos << std::endl;
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else
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std::cout << "Value not found" << std::endl;
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}
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int generate_random_number(int upper_bound){
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return rand() % upper_bound;
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}
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void print_array(int array[], int n){
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for(int i=0;i<n;++i){
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std::cout << array[i] << " ";
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}
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std::cout<<std::endl;
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}
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int splitted_array_search(int split_array[], int lo, int hi, int val, int n){
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// I don't think this will happen, but just in case...
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if(hi<lo)
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return -1;
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// Binary search if the values of hi > lo as the range specified is sorted
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if( split_array[lo] < split_array[hi])
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return binary_search(split_array, lo, hi, val, n);
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print_search(split_array, lo, hi, -1, n);
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int mid = (lo+hi)/2;
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print_search(split_array, lo, hi, mid, n);
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// Get lucky
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if (split_array[mid] == val)
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return mid;
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// Check which side the the mid and query val are at
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// false for left, true for right
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// This is exploiting the fact that the right side is smaller than the left
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bool mid_side, val_side;
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mid_side = split_array[mid] < split_array[0];
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val_side = val < split_array[0];
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// Recurse search, but reduce the range accordingly
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if(mid_side == val_side){
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if (split_array[mid]<val)
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return splitted_array_search(split_array, mid+1, hi, val, n);
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else
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return splitted_array_search(split_array, lo, mid-1, val, n);
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}else{
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if(mid_side)
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return splitted_array_search(split_array, lo, mid-1, val, n);
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else
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return splitted_array_search(split_array, mid+1, hi, val, n);
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}
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}
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int binary_search(int array[], int lo, int hi, int val, int n){
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// Just a normal binary search
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while(lo <= hi){
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print_search(array, lo, hi, -1, n);
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//std::cout << lo << " " << hi << std::endl;
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int mid = (lo+hi)/2;
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print_search(array, lo, hi, mid, n);
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if (array[mid] == val)
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return mid;
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if (array[mid]>val)
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hi = mid-1;
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else
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lo = mid+1;
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}
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return -1;
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}
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void print_search(int split_array[], int lo, int hi, int current, int n){
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for(int i=0; i<n;++i){
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if(i==lo)
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std::cout << "| ";
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if(i==current)
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std::cout << "_ ";
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std::cout<< split_array[i] << " ";
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if(i==current)
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std::cout << "_ ";
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if(i==hi)
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std::cout << "| ";
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}
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std::cout << " \r";
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std::cout.flush();
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usleep(1500000);
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}
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