111. Minimum Depth of Binary Tree（js）

111. 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.

Example:

Given binary tree [3,9,20,null,null,15,7],

    3
   / \
  9  20
    /  \
   15   7

return its minimum depth = 2.

题意：求二叉树的最小深度（根节点到叶子结点的深度最小）

代码如下：

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number}
 */
var minDepth = function(root) {
    if(!root) return 0;
    if(root.left===null && root.right===null) return 1;
    if(root.left===null) return minDepth(root.right)+1;
    else if(root.right===null) return minDepth(root.left)+1;
    else return 1+Math.min(minDepth(root.left),minDepth(root.right));
};