0111 - Minimum Depth of Binary Tree

0111 - Minimum Depth of Binary Tree

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.

Note: A leaf is a node with no children.

Examples

Input: root = [3,9,20,null,null,15,7] Output: 2

Input: root = [2,null,3,null,4,null,5,null,6] Output: 5

Constraints

The number of nodes in the tree is in the range [0, 105]. -1000 <= Node.val <= 1000

Java Solution

Recursion

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public int minDepth(TreeNode root) {
        if(root == null) return 0;
        
        if(root.right == null && root.left == null) return 1;
        
        int minimumDepth = Integer.MAX_VALUE;
        if(root.left != null) {
            minimumDepth = Math.min(minDepth(root.left), minimumDepth);
        }
        if(root.right != null) {
            minimumDepth = Math.min(minDepth(root.right), minimumDepth);
        }
        
        return minimumDepth + 1;
    }
}

BFS Iteration

class Solution {
    public int minDepth(TreeNode root) {
        if(root == null) return 0;
        
        Queue<TreeNode> queue = new ArrayDeque<>();
        queue.offer(root);
        
        int minDepth = 1;
        while(!queue.isEmpty()) {
            int size = queue.size();
            for(int i = 0; i < size; i++) {
                TreeNode current = queue.poll();
                if(current != null && current.left == null && current.right == null) return minDepth;
                if(current.left != null) queue.offer(current.left);
                if(current.right != null) queue.offer(current.right);
            }
            minDepth += 1;
        }
        return -1;
    }
}