Same Tree

描述

Given two binary trees, write a function to check if they are equal or not.

Two binary trees are considered equal if they are structurally identical and the nodes have the same value.

分析

无

递归版

  1. // Same Tree
  2. // 递归版，时间复杂度O(n)，空间复杂度O(logn)
  3. class Solution {
  4. public:
  5.     bool isSameTree(TreeNode *p, TreeNode *q) {
  6.         if (!p && !q) return true;   // 终止条件
  7.         if (!p || !q) return false;  // 剪枝
  8.         return p->val == q->val      // 三方合并
  9.                 && isSameTree(p->left, q->left)
  10.                 && isSameTree(p->right, q->right);
  11.     }
  12. };

迭代版

  1. // Same Tree
  2. // 迭代版，时间复杂度O(n)，空间复杂度O(logn)
  3. class Solution {
  4. public:
  5.     bool isSameTree(TreeNode *p, TreeNode *q) {
  6.         stack<TreeNode*> s;
  7.         s.push(p);
  8.         s.push(q);
  10.         while(!s.empty()) {
  11.             p = s.top(); s.pop();
  12.             q = s.top(); s.pop();
  14.             if (!p && !q) continue;
  15.             if (!p || !q) return false;
  16.             if (p->val != q->val) return false;
  18.             s.push(p->left);
  19.             s.push(q->left);
  21.             s.push(p->right);
  22.             s.push(q->right);
  23.         }
  24.         return true;
  25.     }
  26. };

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原文: https://soulmachine.gitbooks.io/algorithm-essentials/content/cpp/binary-tree/traversal/same-tree.html