c - 在 C 中使用递归二进制搜索查找目标索引

Question

我只能使用给定的参数。一想到要找到目标的索引，我就无法思考。有什么想法吗？

#include <stdio.h>

int RecBinarySearch(int arr[], int len, int target) {

    if (len <= 0)
        return 0; 

    int mid = len/2;

    if (target == arr[mid]){
        return 1;
    }
    if (target < arr[mid]){
        int i=0;
        return RecBinarySearch(arr, mid, target);
    }

    else {
        return RecBinarySearch(arr+mid+1, len-mid-1, target);
    }
}

int main(void){
    int arr[6]={1,2,3,4,5,6};
    int len=sizeof(arr)/sizeof(arr[0]);
    int target = 5;
    RecBinarySearch(arr,len,target);
}

Answer 1

Ideone link

#include <stdio.h>
int RecBinarySearch(int arr[], int len, int target) {
    if(len <= 0) return -1;
    int mid = len / 2;
    if(arr[mid] == target) return mid;
    if(arr[mid] < target) {
        int rightIndex = RecBinarySearch(arr+mid+1, len-mid-1, target);
        return rightIndex == -1 ? -1 : mid+rightIndex+1;
    } else {
        int leftIndex = RecBinarySearch(arr, mid, target);
        return leftIndex == -1 ? -1 : leftIndex;
    }
}

int main(void){
    int arr[6]={1,2,3,4,5,6};
    int len=sizeof(arr)/sizeof(arr[0]);
    int target = 5;
    printf("%d", RecBinarySearch(arr,len,target));
}