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.
Analyse: Compare all nodes in the same place.
1. Recursion
Runtime: 0ms.
1 /** 2 * Definition for a binary tree node. 3 * struct TreeNode { 4 * int val; 5 * TreeNode *left; 6 * TreeNode *right; 7 * TreeNode(int x) : val(x), left(NULL), right(NULL) {} 8 * }; 9 */ 10 class Solution { 11 public: 12 bool isSameTree(TreeNode* p, TreeNode* q) { 13 if(!p && !q) return true; 14 if(!p || !q) return false; //the first line eliminated the situation s.t. both trees are null 15 return p->val == q->val && 16 isSameTree(p->left, q->left) && 17 isSameTree(p->right, q->right); 18 } 19 };
2. Iteration with stack used
Runtime: 0ms.
1 /** 2 * Definition for a binary tree node. 3 * struct TreeNode { 4 * int val; 5 * TreeNode *left; 6 * TreeNode *right; 7 * TreeNode(int x) : val(x), left(NULL), right(NULL) {} 8 * }; 9 */ 10 class Solution { 11 public: 12 bool isSameTree(TreeNode* p, TreeNode* q) { 13 stack<TreeNode* > stk; 14 stk.push(p); 15 stk.push(q); 16 17 while(!stk.empty()){ 18 p = stk.top(); 19 stk.pop(); 20 q = stk.top(); 21 stk.pop(); 22 23 if(!p && !q) continue; 24 if(!p || !q) return false; 25 if(p->val != q->val) return false; 26 27 stk.push(p->left); 28 stk.push(q->left); 29 stk.push(p->right); 30 stk.push(q->right); 31 } 32 return true; 33 } 34 };
3. Iteration with queue used
Runtime: 4ms.
1 /** 2 * Definition for a binary tree node. 3 * struct TreeNode { 4 * int val; 5 * TreeNode *left; 6 * TreeNode *right; 7 * TreeNode(int x) : val(x), left(NULL), right(NULL) {} 8 * }; 9 */ 10 class Solution { 11 public: 12 bool isSameTree(TreeNode* p, TreeNode* q) { 13 queue<TreeNode* > qu; 14 qu.push(p); 15 qu.push(q); 16 17 while(!qu.empty()){ 18 p = qu.front(); 19 qu.pop(); 20 q = qu.front(); 21 qu.pop(); 22 23 if(!p && !q) continue; 24 if(!p || !q) return false; 25 if(p->val != q->val) return false; 26 27 qu.push(p->left); 28 qu.push(q->left); 29 qu.push(p->right); 30 qu.push(q->right); 31 } 32 return true; 33 } 34 };