一、题目思路

        1、先排序数组两段各各取一个索引值：start=0、end=n-1

        2、当start <= end时都需要判断

        3、mid = start + ((end-start)>>1) 防止 start + end 溢出

        4、arr[mid] > num， end = mid - 1；

        5、arr[mid] < num， start = mid + 1；

        6、如不存在，插入时选 end + 1位置插入

二、代码实现

#include <stdio.h>
#include <stdlib.h>int binary_search(int *arr, int size, int num)
{if (!size)return -1;int start = 0;int end = size - 1;while (start <= end) {int mid = start + ((end-start)>>1);if (arr[mid] > num){printf("end = mid %d\n", mid);end = mid - 1;} else if (arr[mid] < num){printf("start = mid %d\n", mid);start = mid + 1;} else {printf("find mid\n");return mid;}}printf("not find, insert index:%d\n", end + 1);return -1;
}void bubble_sort(int *arr, int size)
{int i;int j;for (i = 0; i < size - 1; i++) {for (j = 0; j < size - 1 - i; j++){if (arr[j] > arr[j+1]) {int tmp;tmp = arr[j];arr[j] = arr[j+1];arr[j+1] = tmp;}    }}return;
}void show(int *arr, int size)
{for (int i = 0; i < size; i++) {if (i == size-1)printf("%d\n", arr[i]);elseprintf("%d,", arr[i]);}return;
}int main(int argc, char *argv[])
{int num[] = {33,5,18,1,1,2,9};int size = sizeof(num)/sizeof(int);int num_search = atoi(argv[1]);bubble_sort(num, size);show(num, size);int ret = binary_search(num, size, num_search);printf("%d\n", ret);return 0;
}