二分查找(binary search)算法

//1. 存储在数组中（如果是链表则无法使用二分查找）
//2. 有序的排列 （递增或递减，或重复数都无影响）

//param:有序数组，检索开始为止，结束为止，要查找的数字
//return:返回目标数字所在为止，没有找到返回-1
int binSearch (int arr[], int low, int high, int key) {
    if (low <= high) {
        int mid = (low + high)/2;
        if (key == arr[mid]) return mid;
        else if (key < arr[mid]) return binSearch(arr,low,mid-1,key);
        else if (key > arr[mid]) return binSearch(arr,mid+1,high,key);
    } else return -1;
}

//param:有序数组，数组大小，需要查找的数
//return:查找的数所在位置，找不到返回-1
int binSearch (int *arr, int size, int key) {
    if (arr == NULL || size == 0) return -1;
    int low = 0, high = size -1, mid = 0;
    while (low<=high) {
        mid = (low+high)/2;
        if (arr[mid] < key) low = mid + 1;
        else if (arr[mid] > key) high = mid - 1;
        else return mid;
    }
    return -1;
}