Same tree

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判断两棵树是否相同(结构相同，对应的数值相同)

Same Tree

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显然，这道题可以用DFS

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

这道题第二种解法可以用宽度优先搜索(BFS),此处用栈代替队列

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stack<TreeNode*> stack_p;
        stack<TreeNode*> stack_q;
        if(p)   stack_p.push(p);
        if(q)   stack_q.push(q);
        while(!stack_p.empty() && !stack_q.empty()){
            TreeNode* cur_p=stack_p.top();
            TreeNode* cur_q=stack_q.top();
            stack_p.pop();
            stack_q.pop();
            if(cur_p->val!=cur_q->val) return false;
            if(cur_p->left) stack_p.push(cur_p->left);
            if(cur_q->left) stack_q.push(cur_q->left);
            if(stack_p.size() != stack_q.size())    return false;
            if(cur_p->right) stack_p.push(cur_p->right);
            if(cur_q->right) stack_q.push(cur_q->right);
            if(stack_p.size() != stack_q.size())    return false;
        }
        return stack_p.size() == stack_q.size();