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LeetCode: 100-Same Tree 解題紀錄

Last Updated on 2023-01-11 by Clay

題目

Given the roots of two binary trees p and q, write a function to check if they are the same or not.

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

Example 1:

Input: p = [1,2,3], q = [1,2,3]
Output: true

Example 2:

Input: p = [1,2], q = [1,null,2]
Output: false

Example 3:

Input: p = [1,2,1], q = [1,1,2]
Output: false

Constraints:

  • The number of nodes in both trees is in the range [0, 100].
  • -104 <= Node.val <= 104

題目給定兩顆樹狀結構資料,我們要做的是就是比較兩顆樹,如果完全一致則返回 true、不相同則返回 false


解題思路

遞迴

我們可以直接把題目寫好的 isSameTree() 當作遞迴函式,最基本的案例就是:

  • 比較的兩個節點都是空值(nullptr)-> 返回 true
  • 比較的兩個節點其中一個是空值(nullptr) -> 返回 false
  • 兩個節點值都不相同 -> 返回 false

之後,就是使用遞迴函式跑左右兩邊的節點。


兩節點走訪 複雜度

Time ComplexityO(n)
Space ComplexityO(1)


C++ 範例程式碼

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    bool isSameTree(TreeNode* p, TreeNode* q) {
        // Base case
        if (p == nullptr && q == nullptr) {
            return true;
        }
        else if (p == nullptr || q == nullptr) {
            return false;
        }
        else if (p->val != q->val) {
            return false;
        }

        return isSameTree(p->left, q->left) && isSameTree(p->right, q->right);
    }
};



Python 範例程式碼

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def isSameTree(self, p: Optional[TreeNode], q: Optional[TreeNode]) -> bool:
        # Base case
        if p == None and q == None:
            return True
        elif p == None or q == None:
            return False
        elif p.val != q.val:
            return False

        return self.isSameTree(p.left, q.left) and self.isSameTree(p.right, q.right)

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