[leetcode]Minimum Depth of Binary Tree

树的递归。要注意对左右子树中有null的处理。

/**

 * Definition for binary tree

 * public class TreeNode {

 *     int val;

 *     TreeNode left;

 *     TreeNode right;

 *     TreeNode(int x) { val = x; }

 * }

 */

public class Solution {

    public int minDepth(TreeNode root) {

        // Start typing your Java solution below

        // DO NOT write main() function

        if (root == null) return 0;

        boolean left = root.left != null;

        boolean right = root.right != null;

        

        if(left && right) {

            int minLeft = minDepth(root.left) + 1;

            int minRight = minDepth(root.right) + 1;

            if (minLeft > minRight) return minRight;

            else return minLeft;

        }

        else if (left) {

            return minDepth(root.left) + 1;

        }

        else if (right) {

            return minDepth(root.right) + 1;

        }

        else {

            return 1;

        }

        

    }

}