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.

Analyze

Way1: recursive

陷阱: 需注意的是其中一个子节点为空, 另外一个子节点不为空, 需要以不为空的子节点那边来计数。比如

0
/ \
1 null

此时最短路径为 2 而不是 1。

/**
* 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
const leftRootMinDepth = minDepth(root.left)
const rightRootMinDepth = minDepth(root.right)
if (leftRootMinDepth === 0 || rightRootMinDepth === 0) {
return Math.max(leftRootMinDepth, rightRootMinDepth) + 1
}
return Math.min(leftRootMinDepth, rightRootMinDepth) + 1
};

Sister title

104