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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

递归版

// Same Tree
// 递归版,时间复杂度O(n),空间复杂度O(logn)
public class Solution {
public boolean isSameTree(TreeNode p, TreeNode q) {
if (p == null && q == null) return true; // 终止条件
if (p == null || q == null) return false; // 剪枝
return p.val == q.val // 三方合并
&& isSameTree(p.left, q.left)
&& isSameTree(p.right, q.right);
}
}

迭代版

// Same Tree
// 迭代版,时间复杂度O(n),空间复杂度O(logn)
public class Solution {
public boolean isSameTree(TreeNode p, TreeNode q) {
Stack<TreeNode> s = new Stack<>();
s.push(p);
s.push(q);

while(!s.empty()) {
p = s.pop();
q = s.pop();

if (p == null && q == null) continue;
if (p == null || q == null) return false;
if (p.val != q.val) return false;

s.push(p.left);
s.push(q.left);

s.push(p.right);
s.push(q.right);
}
return true;
}
}

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