虽然Loop永远运行,但不会返回二进制搜索

Question

试图为反向数组输入实现二进制算法.当我执行测试用例时 - 5 4 3 2 1它向我显示一个空白屏幕,即while循环无限运行.随时调试它,但无法弄清楚我哪里出错了.

#include <stdio.h>
#include <stdlib.h>

int findright(int arr[], int key, int low, int high);

void main() {
  int n, i, arr[200], key;
  scanf("%d %d\n", &n, &key);
  for (int i = 0; i < n; i++) {
    scanf("%d", &arr[i]);
  }
  int a = findright(arr, key, 1, n - 1);
  printf("%d", a);
}

int findright(int arr[], int key, int low, int high) {

  int mid = (low + high) / 2;
  while (low <= high) {
    if (arr[mid] == key) {
      return mid;
    } else if (arr[mid] > key) {
      findright(arr, key, mid + 1, high);
    } else {
      findright(arr, key, low, mid - 1);
    }
  }
  return -1;
}

Answer 1

在你的循环中while (low <= high) { ...,值low和high不会改变; 因此,如果循环一旦进入,它将永远不会返回.

当您使用递归时,您将不需要循环:

int findright(int arr[], int key, int low, int high) {

  if (low > high) { // anchor stopping recursion
    return -1;  // indicate that key was not found...
  }

  int mid = (low + high) / 2;
  if (arr[mid] == key) {
      return mid;
  } else if (arr[mid] > key) {
      return findright(arr, key, mid + 1, high);
  } else {
      return findright(arr, key, low, mid - 1);
  }
}

演示.

还要注意的是 - 正如MFisherKDX所提到的那样 - "你的主体中也有一个一个一个错误.你传递1为低,因此永远不会检查第0个元素".