/**
* 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;
LinkedList queue = new LinkedList();
queue.add(root);
int current = 1;
int next = 0;
int depth = 1;
while(!queue.isEmpty()){
TreeNode temp = queue.remove();
if(temp.left == null && temp.right == null) return depth;
if(temp.left!=null){
queue.add(temp.left);
next++;
}
if(temp.right!=null){
queue.add(temp.right);
next++;
}
current--;
if(current == 0){
depth++;
current = next;
next = 0;
}
}
return 0;
}
}