leetcode 100 —— Same Tree

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.

思路：先序遍历，可以设置flag，提前返回。

class Solution {
bool flag = true;
public:
bool isSameTree(TreeNode* p, TreeNode* q) {
preOrder(p, q);
return flag;
}
void preOrder(TreeNode* p, TreeNode *q){
if (!flag||(!p&&!q)) return;
if ((!p&&q) || (p&&!q) || (p->val != q->val)){
flag = false;
return;
}
preOrder(p->left, q->left);
preOrder(p->right, q->right);
}
};