LeetCode - 111. Minimum Depth of Binary Tree

Description

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.

Code

class Solution {
    public int minDepth(TreeNode root) {
        if(root == null) {
            return 0;
        }
        int leftDepth = minDepth(root.left);
        int rightDepth = minDepth(root.right);
        //有个样例是1，2，输出最小高度为2。
        //对于左右子树高度为0的要进行判断。root到最近的叶子节点的高度
        if(leftDepth == 0) {
            return rightDepth+1;
        }
        if(rightDepth == 0) {
            return leftDepth+1;
        }
        return Math.min(leftDepth,rightDepth)+1;
    }
}