mirror of https://github.com/TheAlgorithms/C
110 lines
2.7 KiB
C
110 lines
2.7 KiB
C
/**
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* @file
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* @brief Program to perform [binary
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* search](https://en.wikipedia.org/wiki/Binary_search_algorithm) of a target
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* value in a given *sorted* array.
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* @authors [James McDermott](https://github.com/theycallmemac) - recursive
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* algorithm
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* @authors [Krishna Vedala](https://github.com/kvedala) - iterative algorithm
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*/
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#include <assert.h>
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#include <stdio.h>
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/** Recursive implementation
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* \param[in] arr array to search
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* \param l left index of search range
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* \param r right index of search range
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* \param x target value to search for
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* \returns location of x assuming array arr[l..r] is present
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* \returns -1 otherwise
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*/
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int binarysearch1(const int *arr, int l, int r, int x)
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{
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if (r >= l)
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{
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int mid = l + (r - l) / 2;
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// If element is present at middle
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if (arr[mid] == x)
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return mid;
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// If element is smaller than middle
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if (arr[mid] > x)
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return binarysearch1(arr, l, mid - 1, x);
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// Else element is in right subarray
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return binarysearch1(arr, mid + 1, r, x);
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}
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// When element is not present in array
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return -1;
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}
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/** Iterative implementation
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* \param[in] arr array to search
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* \param l left index of search range
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* \param r right index of search range
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* \param x target value to search for
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* \returns location of x assuming array arr[l..r] is present
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* \returns -1 otherwise
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*/
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int binarysearch2(const int *arr, int l, int r, int x)
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{
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int mid = l + (r - l) / 2;
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while (arr[mid] != x)
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{
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if (r <= l || r < 0)
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return -1;
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if (arr[mid] > x)
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// If element is smaller than middle
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r = mid - 1;
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else
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// Else element is in right subarray
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l = mid + 1;
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mid = l + (r - l) / 2;
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}
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// When element is not present in array
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return mid;
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}
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/** Test implementations */
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void test()
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{
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// give function an array to work with
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int arr[] = {2, 3, 4, 10, 40};
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// get size of array
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int n = sizeof(arr) / sizeof(arr[0]);
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printf("Test 1.... ");
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// set value to look for
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int x = 10;
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// set result to what is returned from binarysearch
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int result = binarysearch1(arr, 0, n - 1, x);
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assert(result == 3);
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printf("passed recursive... ");
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result = binarysearch2(arr, 0, n - 1, x);
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assert(result == 3);
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printf("passed iterative...\n");
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printf("Test 2.... ");
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x = 5;
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// set result to what is returned from binarysearch
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result = binarysearch1(arr, 0, n - 1, x);
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assert(result == -1);
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printf("passed recursive... ");
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result = binarysearch2(arr, 0, n - 1, x);
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assert(result == -1);
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printf("passed iterative...\n");
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}
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/** Main function */
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int main(void)
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{
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test();
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return 0;
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}
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