leetcode---树专题

题目1： 求一棵二叉树的最大深度 

Given a binary tree, find its maximum depth. The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
//求二叉树的最大深度
public class Solution {
    public int maxDepth(TreeNode root) {
        if(root==null)          
            return 0;
        int lDepth= maxDepth(root.left);
        int rDepth= maxDepth(root.right);
        return  1+( lDepth>rDepth ? lDepth: rDepth);   //左右子树 选最大深度者（即使一侧没有节点也没关系  肯定选最大的 和0无关）
    }
}

题目2：求一棵二叉树的最小深度（需要考虑一侧无子节点情况）

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.

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public int run(TreeNode root) {   
        if(root==null)
            return 0; 
        int lDepth=run(root.left);
        int rDepth=run(root.right);
        if(lDepth==0 || rDepth==0)    //需要考虑可能没有一侧子节点的情况  这样最小的是0  但只有根节点  不能算是到叶子节点的最短路径
            return lDepth+rDepth+1;
        return 1+(lDepth< rDepth? lDepth: rDepth);
    }
}