LeetCode 0111 Minimum Depth of Binary Tree【二叉树，最小深度，递归】

Given a binary tree, find its minimum depth.

The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node.

Note: A leaf is a node with no children.

Example:

Given binary tree [3,9,20,null,null,15,7],

    3
   / \
  9  20
    /  \
   15   7

return its minimum depth = 2.

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题意

注意需要是到叶子结点

思路1

代码1

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int minDepth(TreeNode* root) {
        if(root == NULL) return 0;
        int l = minDepth(root->left);
        int r = minDepth(root->right);
        if(l == 0 || r == 0) return l + r + 1;
        return min(l, r) + 1;
    }
};