binary search - c

binary search - c (simple)

 

search - basic:

 

/** @author [e-mail] */
#include <stdio.h>
/**
 * binary search (simple)
 *
 * @param 
 * 	arr	pointer of array
 * @param 
 * 	len	length of array
 * @param 
 *	x	target to search
 *
 * @return
	index of target in the array,return -1 if not found, 
 */
int bin_search(int *arr,int len,int x) {
	// indexs 
	int start = 0,end = len-1,middle;
	while (end >= start) {
		middle = (start + end) >> 1;
		if (*(arr+middle)==x) {
			return middle;
		} else if(x < *(arr+middle)) {
			end = middle - 1;
		} else {
			start = middle + 1;
		}
	}
	// not found
	return -1;
}

int main() {
	int arr_1[8] = {0,1,3,4,6,7,9,10};
	int i_1 = bin_search(arr_1,8,3);
	int i_2 = bin_search(arr_1,8,9);
	int i_3 = bin_search(arr_1,8,5);
	int i_4 = bin_search(arr_1,8,15);
	int i_5 = bin_search(arr_1,8,-5);
	printf("expect:\n\t2,6,-1,-1,-1\n");
	printf("actural:\n\t%d,%d,%d,%d,%d\n",i_1,i_2,i_3,i_4,i_5);
}

 

 

search - first / last / all

/** @author [e-mail] */
#include <stdio.h>
/**
 * binary search, search the first match,
 *
 * @param 
 * 	arr	pointer of array
 * @param 
 * 	len	length of array
 * @param 
 *	x	target to search
 *
 * @return
	index where target first appear in the array,return -1 if not found, 
 */
int bin_search_first(int *arr,int len,int x) {
	// indexs 
	int start = 0,end = len-1,middle;
	while (end > start) { // here must be '>', not '>=', otherwise endless loop might happen,
		middle = (start + end) >> 1;
		if(*(arr+middle) < x) {
			start = middle + 1;
		} else {
			end = middle;
		}
	}
	if(*(arr+start) == x) {
		return start;
	} else {
		// not found
		return -1;
	}
}

int test_search_first() {
	int len = 17;
	int arr_1[17] = {0,1,3,4,6,7,7,7,7,7,7,7,7,7,7,9,10};
	int i_0 = bin_search_first(arr_1,len,7);
	int i_1 = bin_search_first(arr_1,len,3);
	int i_2 = bin_search_first(arr_1,len,9);
	int i_3 = bin_search_first(arr_1,len,5);
	int i_4 = bin_search_first(arr_1,len,15);
	int i_5 = bin_search_first(arr_1,len,-5);
	printf("expect:\n\t5,2,15,-1,-1,-1\n");
	printf("actural:\n\t%d,%d,%d,%d,%d,%d\n",i_0,i_1,i_2,i_3,i_4,i_5);
}

/**
 * binary search, search the last match,
 *
 * @param 
 * 	arr	pointer of array
 * @param 
 * 	len	length of array
 * @param 
 *	x	target to search
 *
 * @return
	index where target last appear in the array,return -1 if not found, 
 */
int bin_search_last(int *arr,int len,int x) {
	// indexs 
	int start = 0,end = len-1,middle;
	while (end > start) { // here must be '>', not '>=', otherwise endless loop might happen,
		middle = (start + end + 1) >> 1; // here must be '(start + end + 1)', not '(start + end)', otherwise endless loop might happen,
		if(*(arr+middle) > x) {
			end = middle - 1;
		} else {
			start = middle;
		}
	}
	if(*(arr+end) == x) {
		return end;
	} else {
		// not found
		return -1;
	}
}

int test_search_last() {
	int len = 17;
	int arr_1[17] = {0,1,3,4,6,7,7,7,7,7,7,7,7,7,7,9,10};
	int i_0 = bin_search_last(arr_1,len,7);
	int i_1 = bin_search_last(arr_1,len,3);
	int i_2 = bin_search_last(arr_1,len,9);
	int i_3 = bin_search_last(arr_1,len,5);
	int i_4 = bin_search_last(arr_1,len,15);
	int i_5 = bin_search_last(arr_1,len,-5);
	printf("expect:\n\t14,2,15,-1,-1,-1\n");
	printf("actural:\n\t%d,%d,%d,%d,%d,%d\n",i_0,i_1,i_2,i_3,i_4,i_5);
}

/**
 * result of search all match,
 * first is the index of first match, -1 means no match
 * last is the index of last match, -1 means no match
 * count is the count of match,
 */
typedef struct {int first, last, count;} all_result;

/**
 * binary search, search all match,
 * steps:
 	* first search a match,
	* if not found, then return, over,
	* if found,
		divide the array into 2 part by the found match, 
		search in left part for the first match,and search in the right part for the last match, 
		then combine them, that's the result,
 *
 * @param 
 * 	arr	pointer of array
 * @param 
 * 	len	length of array
 * @param 
 *	x	target to search
 *
 * @return
 	type all_result
 */
all_result * bin_search_all(int *arr,int len,int x) {
	// indexs 
	int start = 0,end = len-1,middle;
	static all_result result;
	result.first = -1;result.last = -1;result.count = 0; // this is a static variable, init it every time,
	while (end >= start) {
		middle = (start + end) >> 1;
		if (*(arr+middle)==x) { // find a match
			result.first = bin_search_first(arr+start,middle-start+1,x)+start;
			result.last = bin_search_last(arr+middle, end-middle+1,x)+middle;
			result.count = result.last - result.first + 1;
			return &result;
		} else if(x < *(arr+middle)) {
			end = middle - 1;
		} else {
			start = middle + 1;
		}
	}
	return &result;
}

int test_search_all() {
	int len = 17;
	int arr_1[17] = {0,1,3,4,6,7,7,7,7,7,7,7,7,7,7,9,10};

	all_result *r_0 = bin_search_all(arr_1,len,7);
	printf("r_0\texpect: [5, 14]:10,\tactrual: [%d, %d]:%d\n",r_0->first,r_0->last,r_0->count);

	all_result *r_1 = bin_search_all(arr_1,len,3);
	printf("r_1\texpect: [2, 2]:1,\tactrual: [%d, %d]:%d\n",r_1->first,r_1->last,r_1->count);
	
	all_result *r_2 = bin_search_all(arr_1,len,9);
	printf("r_2\texpect: [15, 15]:1,\tactrual: [%d, %d]:%d\n",r_2->first,r_2->last,r_2->count);
	
	all_result *r_3 = bin_search_all(arr_1,len,5);
	printf("r_3\texpect: [-1, -1]:0,\tactrual: [%d, %d]:%d\n",r_3->first,r_3->last,r_3->count);
	
	all_result *r_4 = bin_search_all(arr_1,len,15);
	printf("r_4\texpect: [-1, -1]:0,\tactrual: [%d, %d]:%d\n",r_4->first,r_4->last,r_4->count);
	
	all_result *r_5 = bin_search_all(arr_1,len,-5);
	printf("r_5\texpect: [-1, -1]:0,\tactrual: [%d, %d]:%d\n",r_5->first,r_5->last,r_5->count);
}

int main() {
	test_search_all();
}