题目地址：

https://leetcode.com/problems/check-if-two-expression-trees-are-equivalent/

给定两个只含'+'和英文小写字母作为运算数的表达式树，问这两个表达式树所对应的表达式是否等价。等价的含义是两个表达式作为代数式用等号连起来是恒等式。

只需要数一下两个表达式树所含字母的类型、数量都相同即可。代码如下：

public class Solution {public boolean checkEquivalence(Node root1, Node root2) {int[] count = new int[26];dfs(root1, count, 1);dfs(root2, count, -1);for (int i = 0; i < count.length; i++) {if (count[i] != 0) {return false;}}return true;}private void dfs(Node cur, int[] count, int diff) {if (cur == null) {return;}if (cur.val != '+') {count[cur.val - 'a'] += diff;}dfs(cur.left, count, diff);dfs(cur.right, count, diff);}
}class Node {char val;Node left, right;public Node(char val) {this.val = val;}
}

时间复杂度 O ( n ) O(n) O(n)，空间 O ( h ) O(h) O(h)。

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【Leetcode】1612. Check If Two Expression Trees are Equivalent

题目地址：

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