迭代----- Maximum Depth of Binary Tree

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.

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Example
Given a binary tree as follow:

1
/ \
2 3
/ \
4 5
The maximum depth is 3.

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解法0:

/** * Definition of TreeNode: * public class TreeNode { *     public int val; *     public TreeNode left, right; *     public TreeNode(int val) { *         this.val = val; *         this.left = this.right = null; *     } * } */public class Solution {    public int maxDepth(TreeNode root) {        if (root == null) {            return 0;        }        int left = maxDepth(root.left);        int right = maxDepth(root.right);        return Math.max(left, right) + 1;    }}

解法1:

/** * Definition of TreeNode: * public class TreeNode { *     public int val; *     public TreeNode left, right; *     public TreeNode(int val) { *         this.val = val; *         this.left = this.right = null; *     } * } */public class Solution {    /**     * @param root: The root of binary tree.     * @return: An integer.     */    public int maxDepth(TreeNode root) {    if(root == null)        return 0;    int depth = 0;    LinkedList<TreeNode> queue = new LinkedList<TreeNode>();    queue.add(root);    int curNum = 1; //num of nodes left in current level    int nextNum = 0; //num of nodes in next level    while(!queue.isEmpty()){        TreeNode n = queue.poll();        curNum--;        if(n.left!=null){            queue.add(n.left);            nextNum++;        }        if(n.right!=null){            queue.add(n.right);            nextNum++;        }        if(curNum == 0){            curNum = nextNum;            nextNum = 0;            depth++;        }    }    return depth;}}