/**

* Definition for a binary tree node.

* function TreeNode(val, left, right) {

* this.val = (val===undefined ? 0 : val)

* this.left = (left===undefined ? null : left)

* this.right = (right===undefined ? null : right)

* } */

var minDepth = function (root) {

//recursive

if (!root) return 0;

else if (!root.left && !root.right) return 1;

else if (!root.left) return 1 + minDepth(root.right);

else if (!root.right) return 1 + minDepth(root.left);

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

//Iterative approach

// if (!root) return 0;

// const que = [root];

// let minDepth = 1;

// while (que.length > 0) {

// let level = que.length;

// for (let i = 0; i < level; i++) {

// const curr = que.shift();

// if (!curr.left && !curr.right) return minDepth;

// if (curr.left) que.push(curr.left);

// if (curr.right) que.push(curr.right);

// }

// minDepth++;

// }

// return minDepth;

};