#111 Minimum Depth of Binary Tree & #104 Maximum Depth of Binary Tree

#111 Minimum Depth of Binary

题目：

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.

题解：

我用的递归解法。

/**
* Definition for a binary tree node.
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public int minDepth(TreeNode root) {
if(root == null)return 0;
if(root.left == null)return minDepth(root.right)+1;
if(root.right == null)return minDepth(root.left)+1;
return Math.min(minDepth(root.left),minDepth(root.right))+1;
}
}

还有一种BFS的解法，用的迭代。网上找的程序：http://blog.csdn.net/sbitswc/article/details/26526031。

public int minDepthBFS(TreeNode root){
if(root == null) return 0;
ArrayList<TreeNode> last = new ArrayList<TreeNode>();
last.add(root);
int count =1;
while(!last.isEmpty()){
ArrayList<TreeNode> cur = new ArrayList<TreeNode>();
for (TreeNode treeNode : last) {
if(treeNode.left == null && treeNode.right == null) return count;
if(treeNode.left != null) cur.add(treeNode.left);
if(treeNode.right != null) cur.add(treeNode.right);
}
count++;
last = new ArrayList<TreeNode>(cur);
}
return count;
}

#104 Maximum Depth of Binary Tree

题目：

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.
题解：

/**
* Definition for a binary tree node.
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public int maxDepth(TreeNode root) {
if(root == null)return 0;
return Math.max(maxDepth(root.left),maxDepth(root.right))+1;
}
}