[GeeksForGeeks] Find Minimum Depth of a Binary Tree

Give a binary tree, find its minimum depth. 

The minimum depth is the number of nodes along the shortest path from root node down to the nearest leaf node.

 

Solution 1. Recursion 

 1 public class MinDepthBt {
 2     public int getMinDepth(TreeNode root) {
 3         return helper(root, 0);
 4     }
 5     private int helper(TreeNode node, int depth) {
 6         if(node == null) {
 7             return depth;
 8         }
 9         return Math.min(helper(node.left, depth + 1), helper(node.right, depth + 1));
10     }
11 }

 

Solution 2. Level order traversal, found the first leaf node and return its level.

This solution is better than the recursive solution because we don't need to traverse all nodes.

 

 1 import java.util.LinkedList;
 2 import java.util.Queue;
 3 
 4 public class MinDepthBt {
 5     public int getMinDepth(TreeNode root) {
 6         if(root == null) {
 7             return 0;
 8         }
 9         if(root.left == null || root.right == null) {
10             return 1;
11         }
12         Queue<TreeNode> queue = new LinkedList<TreeNode>();
13         queue.add(root);
14         int currLevel = 1; int minLevel = 1;
15         boolean minDepthFound = false;
16         while(!minDepthFound && !queue.isEmpty()) {
17             int size = queue.size();
18             for(int i = 0; i < size; i++) {
19                 TreeNode curr = queue.poll();
20                 if(curr.left == null && curr.right == null) {
21                     minDepthFound = true;
22                     minLevel = currLevel;
23                     break;
24                 }
25                 if(curr.left != null) {
26                     queue.offer(curr.left);
27                 }
28                 if(curr.right != null) {
29                     queue.offer(curr.right);
30                 }
31             }
32             currLevel++;
33         }
34         return minLevel;
35     }
36 }

 

posted @ 2017-08-19 04:05  Review->Improve  阅读(147)  评论(0)  编辑  收藏  举报