LeetCode 二叉树的最小深度 111

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.

思路

1.如果根为空的话，返回0就可以了

2.如果左子树和右子树都不为空的话，返回最小深度

3.如果左子树或者右子树为空的话，那么就返回不为空的子树的深度

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */
int minDepth(struct TreeNode* root) {
    if(!root) return 0;
    int left = minDepth(root->left);
    int right = minDepth(root->right);
    if(root->left && root->right) return left < right ? left + 1 : right + 1;
    else return left + right + 1;
}