572. Subtree of Another Tree

Description

Given two non-empty binary trees s and t, check whether tree t has exactly the same structure and node values with a subtree of s. A subtree of s is a tree consists of a node in s and all of this node's descendants. The tree s could also be considered as a subtree of itself.

Example 1: Given tree s:

     3
    / \
   4   5
  / \
 1   2

Given tree t:

   4 
  / \
 1   2

Return true, because t has the same structure and node values with a subtree of s.

Example 2: Given tree s:

     3
    / \
   4   5
  / \
 1   2
    /
   0

Given tree t:

   4
  / \
 1   2

Return false.

Solution

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * Traverse the binary tree with Depth-First Search (DFS) algorithm (preorder)
 * @param {TreeNode} s
 * @param {TreeNode} t
 * @return {boolean}
 */
var isSubtree = function(s, t) {
    "use strict";
    function match(node1, node2) {
        if (node1 && node2) {
            if (node1.val === node2.val) {
                return match(node1.left, node2.left) &&
                    match(node1.right, node2.right);
            } else {
                return false;
            }
        } else {
            return node1 === node2;
        }
    }
    function dfs(node) {
        if (node) {
            if (node.val === t.val) {
                if (match(node, t)) {
                    return true;
                }
            }
            return dfs(node.left) || dfs(node.right);
        }
    }
    return dfs(s) || false;
};