Problem111.java

import java.util.LinkedList;
import java.util.Queue;

class Problem111 {

 public static void main(String[] args) {
 Problem111 p = new Problem111();
 TreeNode root = new TreeNode(1);
 //root.left = new TreeNode(2);
 //root.right = new TreeNode(3);
 //root.left.right = new TreeNode(4);
 System.out.println(p.minDepth(root));
 }

 public int minDepth(TreeNode root) {

 int depth = 0;
 if (root == null) {
 return depth;
 }

 if (root.left == null && root.right == null) {
 return 1;
 }

 Queue<TreeNode> queue = new LinkedList<>();
 queue.add(root);
 int level = 1;
 int count = 0;
 while(queue.size() > 0) {
 count = queue.size();
 while(count>0) {
 count--;
 TreeNode t = queue.poll();
 if (t.left == null && t.right == null) return level;
 if (t.left != null) {
 queue.add(t.left);
 }
 if (t.right != null) {
 queue.add(t.right);
 }
 }
 level++;
 }
 return 0;
 }
}