# Minimum Depth of Binary Tree

## Question

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


## 題解

### Java

/**
* 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.
*/
public int minDepth(TreeNode root) {
if (root == null) return 0;

int leftDepth = minDepth(root.left);
int rightDepth = minDepth(root.right);

// current node is not leaf node
if (root.left == null) {
return 1 + rightDepth;
} else if (root.right == null) {
return 1 + leftDepth;
}

return 1 + Math.min(leftDepth, rightDepth);
}
}


### C++

/**
* Definition for a binary tree node.
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
int depth(TreeNode* n){
if(!n->left and !n->right) return 1;
if(!n->left) return 1 + depth(n->right);
if(!n->right) return 1 + depth(n->left);
return 1 + min(depth(n->left), depth(n->right));
}
int minDepth(TreeNode* root) {
if(!root) return 0;
return depth(root);
}
};


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