LeetCode111 二叉树的最小深度

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

public int minDepth(TreeNode root) {
        if(root == null) return 0;
        if(root.left != null && root.right != null){
            return Math.min(minDepth(root.left), minDepth(root.right)) + 1;
        }
        else if(root.left != null){  //如果条件写成minDepth(root.left != 0会超时，尽量少写递归函数)
            return minDepth(root.left) + 1;
        }
        else if(root.right != null){
            return minDepth(root.right) + 1;
        }
        return 1;
    }