/*

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.

Example

Given a binary tree as follow:

1

/ \

2 3

/ \

4 5

The minimum depth is 2

Tags Expand

Depth First Search

Thinking Process:

Note: a little different from maxDepth:

If 1,#,2: the left route 1-# does not count as a path, so the minDepth is actually 2 in this example.

We need a helper function to calculate the minimum.

*/

/**

* 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.

*/

//recursive:

public int minDepth(TreeNode root) {

if (root == null) {

return 0;

}

return getMin(root);

}

public int getMin(TreeNode root) {

if (root == null) {

return Integer.MAX_VALUE;

}

if (root.left == null && root.right == null) {

return 1;

}

return Math.min(getMin(root.left), getMin(root.right)) + 1;

}

}