something about basic usage of vector,queue
时间：2014-04-30 18:47:20
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1.for a two dimension vector, we must assign at least the first dimension of the vector
2.each dimension of an inner vector can be different
3.if you don‘t want to set a volume for vector<vector<int> > for uncertainness, you can just use a method like append to implement the structure,which is applied inBinary Tree Level Order Traversal,
4.about queue: to add an element, q.push(element); to get the first element, q.front(); to erase the first element, q.pop();
5.how to differ elements from different layers?
use two queues rather than one
code：
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class
Solution{public: vector<vector<int> > levelOrder(TreeNode*root){ vector<vector<int> > matrix; if(root == NULL){ return
matrix; } queue<TreeNode*> qNode[2]; //int row = 0; qNode[0].push(root); int
index = 0; while((!qNode[0].empty())||(!qNode[1].empty())){ vector<int>mm; switch(index){ case(0): while(!qNode[0].empty()){ TreeNode* tmp = qNode[0].front(); qNode[0].pop(); mm.push_back(tmp->val); if(tmp->left != NULL){ qNode[1].push(tmp->left); } if(tmp->right != NULL){ qNode[1].push(tmp->right); } } index = 1 - index; matrix.push_back(mm); //++row; break; case(1): //vector<vector<int> >m; while(!qNode[1].empty()){ TreeNode* tmp = qNode[1].front(); qNode[1].pop(); //matrix[row].push_back(tmp->val); mm.push_back(tmp->val); if(tmp->left != NULL){ qNode[0].push(tmp->left); } if(tmp->right!=NULL){ qNode[0].push(tmp->right); } } index = 1 - index; //++row; matrix.push_back(mm); } } return
matrix; }}; |
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