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100. Same Tree

Description

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

Solutions

Solution 1: DFS

We can use the DFS recursive method to solve this problem.

First, determine whether the root nodes of the two binary trees are the same. If both root nodes are null, then the two binary trees are the same. If only one of the root nodes is null, then the two binary trees are definitely different. If both root nodes are not null, then determine whether their values are the same. If they are not the same, then the two binary trees are definitely different. If they are the same, then determine whether the left subtrees of the two binary trees are the same and whether the right subtrees are the same. The two binary trees are the same only when all the above conditions are met.

The time complexity is $O(\min(m, n))$, and the space complexity is $O(\min(m, n))$. Here, $m$ and $n$ are the number of nodes in the two binary trees, respectively. The space complexity mainly depends on the number of layers of recursive calls, which will not exceed the number of nodes in the smaller binary tree.

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# 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:
        if p == q:
            return True
        if p is None or q is None or p.val != q.val:
            return False
        return self.isSameTree(p.left, q.left) and self.isSameTree(p.right, q.right)

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/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public boolean isSameTree(TreeNode p, TreeNode q) {
        if (p == q) return true;
        if (p == null || q == null || p.val != q.val) return false;
        return isSameTree(p.left, q.left) && isSameTree(p.right, q.right);
    }
}

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/**
 * 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) {
        if (p == q) return true;
        if (!p || !q || p->val != q->val) return false;
        return isSameTree(p->left, q->left) && isSameTree(p->right, q->right);
    }
};

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/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func isSameTree(p *TreeNode, q *TreeNode) bool {
    if p == q {
        return true
    }
    if p == nil || q == nil || p.Val != q.Val {
        return false
    }
    return isSameTree(p.Left, q.Left) && isSameTree(p.Right, q.Right)
}

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/**
 * Definition for a binary tree node.
 * class TreeNode {
 *     val: number
 *     left: TreeNode | null
 *     right: TreeNode | null
 *     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
 *         this.val = (val===undefined ? 0 : val)
 *         this.left = (left===undefined ? null : left)
 *         this.right = (right===undefined ? null : right)
 *     }
 * }
 */

function isSameTree(p: TreeNode | null, q: TreeNode | null): boolean {
    if (p == null && q == null) {
        return true;
    }
    if (p == null || q == null || p.val !== q.val) {
        return false;
    }
    return