二分法

#include<stdio.h>
int binary_search(int arr[], int k, int sz) {

	int left = 0;
	int right = sz - 1;
	while (left <= right) {
		int mid = (left + right) / 2;
		if (arr[mid] < k)
		{
			left = mid + 1;
		}
		else if (arr[mid] > k) {
			right = mid - 1;
		}
		else {
			return mid;

		}
	}return -1;
}
int main() {
	int arr[10] = { 1,2,3,4,5,6,7,8,9,10 };
	int k = 7;
	int sz = sizeof(arr) / sizeof(arr[0]);
	int ret = binary_search( arr,  k,  sz);
	if (ret == -1) {
		printf("找不到指定的数字\n");
	}
	else {
		printf("找到了，下标是:%d\n", ret);
	}
	return 0;
}