# Minimum Depth of Binary Tree

ID: 111; easy

## Solution 1 (Go)

``````/**
* Definition for a binary tree node.
* type TreeNode struct {
*     Val int
*     Left *TreeNode
*     Right *TreeNode
* }
*/
func minDepth(root *TreeNode) int {
if root == nil {
return 0
}
if root.Right == nil {
return minDepth(root.Left) + 1
}
if root.Left == nil {
return minDepth(root.Right) + 1
}
return min(minDepth(root.Left), minDepth(root.Right)) + 1
}

func min(x, y int) int {
if x < y {
return x
}
return y
}``````

## Solution 2 (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;
if (root.left == null)
return minDepth(root.right) + 1;
if (root.right == null)
return minDepth(root.left) + 1;
int leftDepth = minDepth(root.left);
int rightDepth = minDepth(root.right);
return Math.min(leftDepth, rightDepth) + 1;
}
}``````

### Notes

• Divide and conquer

## Solution 3 (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;
return minDepthHelper(root);
}

private int minDepthHelper(TreeNode root) {
if (root == null)
return Integer.MAX_VALUE;
if (root.left == null && root.right == null)
return 1;
return Math.min(minDepthHelper(root.left), minDepthHelper(root.right)) + 1;

}
}``````

### Notes

• Divide and conquer slight variant

## Solution 4 (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 {

private int ans = Integer.MAX_VALUE;

/**
* @param root: The root of binary tree
* @return: An integer
*/
public int minDepth(TreeNode root) {
if (root == null) return 0;
dfs(root, 1);
return ans;
}

private void dfs(TreeNode root, int depth) {
if (root == null) return;
if (root.left == null && root.right == null) {
ans = Math.min(ans, depth);
return;
}
dfs(root.left, depth + 1);
dfs(root.right, depth + 1);
}

}``````

• Traversal

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