2

我创建了一个包含 1000 个元素的向量，元素的值是索引本身 V[100] = 100，V[50] = 50 等。

当我通过值调用二进制搜索时，它必须返回给我的索引，所以 binary_search(vector, begin, end, 50) 必须返回给我 50，但返回 30。我尝试使用 gdb 进行调试，但可以没发现有什么不对。

代码：

int rbb(int *v, int left, int right, int val) 
{

    int mid = (left + right) / 2;  //middle element

    if (right < left) //stop codition, pointers shifted
        return -1;

    if (val == v[mid]) //found value
        return mid;  

    if (val > v[mid]) //value is on vector right portion
        rbb(v, mid+1, right, val);

    if (val < v[mid]) //value is on vector left portion
        rbb(v, left, mid-1, val);

}

int main () 
{

    int v[1000];

    for (int i = 0; i < 1000; i++)
        v[i] = i;

    int x = rbb(v, 0, 999, 300);
    printf("%d", x);
}
4

4 回答 4

4

您的代码的问题是，如果 rbb 函数，您没有从递归调用返回值。你应该修改你的代码

if (val > v[mid]) //value is on vector right portion
    return rbb(v, mid+1, right, val);

if (val < v[mid]) //value is on vector left portion
    return rbb(v, left, mid-1, val);
于 2019-11-02T04:21:36.997 回答
0

你可以试试这个

int rbb(int *v, int left, int right, int val) {

int mid = (left + right) / 2;  //middle element

if (right < left) //stop codition, pointers shifted
    return -1;

èlse if (val == v[mid]) //found value
    return mid;  

else if (val > v[mid]) //value is on vector right portion
    rbb(v, mid+1, right, val);

else if (val < v[mid]) //value is on vector left portion
    rbb(v, left, mid-1, val);
}



int main () {

int v[1000];

for (int i = 0; i < 1000; i++)
    v[i] = i;

int x = rbb(v, 0, 999, 300);
printf("%d", x);
}
于 2019-11-02T04:14:18.570 回答
-1

问题在于回报。当函数返回时，它不会结束并继续调用其他 if 语句来更改 mid 变量。你可以这样改变


    int rbb (int *v, int left, int right, int val){
        int mid = (left + right) / 2;  //middle element

        if (right < left) //stop codition, pointers shifted
            return -1;

        else if (val == v[mid]) //found value
            return mid;

        else if (val > v[mid]) //value is on vector right portion
            rbb(v, mid+1, right, val);

        else if (val < v[mid]) //value is on vector left portion
            rbb(v, left, mid-1, val);
    }

    int main() {
        int v[1000];

        for (int i = 0; i < 1000; i++)
            v[i] = i;

        int x = rbb(v, 0, 999, 300);
        printf("%d", x);
    }
于 2019-11-02T04:34:46.207 回答
-1

你可以使用这个代码，你的代码也是正确的，但你应该在比较时使用 else if 语句......

有一个美好的一天享受编码

#include<stdio.h>
int rbb(int v[], int left, int right, int val);
int main ()
{
int i,v[1000],x;
   for (i = 0; i <1000; i++)
     {
        v[i] = i;
     }
     x = rbb(v, 0,999, 300);
     printf("%d", x);

}
int rbb(int v[], int left, int right, int val) {
int mid;
mid = (left + right) / 2;  //middle element
if (right < left) //stop codition, pointers shifted
   {
      return 1;
   }
else if (val == v[mid]) //found value
   {    
      return mid;
   }
else if (val > v[mid]) //value is on vector right portion
    {
        rbb(v, mid+1, right, val);
    }
else//value is on vector left portion
    {
        rbb(v, left, mid-1, val);
    }

}
于 2019-11-02T06:54:03.913 回答