二分查找：根据索引二分，循环查找的条件是左索引小于等于右索引。

二叉树需要判断自身根是否为NULL，并通过改变current的值进行判断。

#include <iostream>
using namespace std;
// 长度为 N 的有序表nums 中查找 target
int BiSearch(int *nums, int N, int target)
{int l = 0, r = N - 1;while (l <= r){int mid = (l + r) / 2;if (target == nums[mid]){return mid;}if (target < nums[mid]){r = mid - 1;}if (target > nums[mid]){l = mid + 1;}}return -1;
}
// 二叉树
typedef struct TreeNode
{int data;struct TreeNode *left, *right;
} TreeNode;
TreeNode *SearchTree(TreeNode *root, int target)
{if (!root){return NULL;}TreeNode *current = root;while (current){if (target == current->data){return current;}if (target < current->data){current = current->left;}else{current = current->right;}}return NULL;
}
int main()
{int nums[10] = {1, 3, 5, 7, 9, 11, 13, 15, 17, 19};cout << BiSearch(nums, 10, 5) << endl;return 0;
}