1086. Tree Traversals Again (25)
2015-09-08 22:18
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题目链接:http://www.patest.cn/contests/pat-a-practise/1086
题目:
An inorder binary tree traversal can be implemented in a non-recursive way with a stack. For example, suppose that when a 6-node binary tree (with the keys numbered from 1 to 6) is traversed, the stack operations are: push(1); push(2); push(3); pop(); pop();
push(4); pop(); pop(); push(5); push(6); pop(); pop(). Then a unique binary tree (shown in Figure 1) can be generated from this sequence of operations. Your task is to give the postorder traversal sequence of this tree.
Figure 1
Input Specification:
Each input file contains one test case. For each case, the first line contains a positive integer N (<=30) which is the total number of nodes in a tree (and hence the nodes are numbered from 1 to N). Then 2N lines follow, each describes a stack operation in
the format: "Push X" where X is the index of the node being pushed onto the stack; or "Pop" meaning to pop one node from the stack.
Output Specification:
For each test case, print the postorder traversal sequence of the corresponding tree in one line. A solution is guaranteed to exist. All the numbers must be separated by exactly one space, and there must be no extra space at the end of the line.
Sample Input:
Sample Output:
分析:
思路:构建一个stack,其中其top就是当前节点,后添加的节点是其孩子,如果左孩子非空就添加到右孩子。
AC代码:
截图:
——Apie陈小旭
题目:
An inorder binary tree traversal can be implemented in a non-recursive way with a stack. For example, suppose that when a 6-node binary tree (with the keys numbered from 1 to 6) is traversed, the stack operations are: push(1); push(2); push(3); pop(); pop();
push(4); pop(); pop(); push(5); push(6); pop(); pop(). Then a unique binary tree (shown in Figure 1) can be generated from this sequence of operations. Your task is to give the postorder traversal sequence of this tree.
Figure 1
Input Specification:
Each input file contains one test case. For each case, the first line contains a positive integer N (<=30) which is the total number of nodes in a tree (and hence the nodes are numbered from 1 to N). Then 2N lines follow, each describes a stack operation in
the format: "Push X" where X is the index of the node being pushed onto the stack; or "Pop" meaning to pop one node from the stack.
Output Specification:
For each test case, print the postorder traversal sequence of the corresponding tree in one line. A solution is guaranteed to exist. All the numbers must be separated by exactly one space, and there must be no extra space at the end of the line.
Sample Input:
6 Push 1 Push 2 Push 3 Pop Pop Push 4 Pop Pop Push 5 Push 6 Pop Pop
Sample Output:
3 4 2 6 5 1
分析:
思路:构建一个stack,其中其top就是当前节点,后添加的节点是其孩子,如果左孩子非空就添加到右孩子。
AC代码:
#include<cstdio> #include<iostream> #include<stack> #include<string> using namespace std; struct Node{ int data; Node* lchild; Node* rchild; Node(int num):data(num),lchild(NULL),rchild(NULL){} Node():lchild(NULL),rchild(NULL){}//不要忘了写上默认构造函数,否则孩子不为空,判断会有误 }; Node* createTree(int nn){ stack<Node*>Node_Stack; Node* ret = new Node(); string str_tmp; cin >> str_tmp; int i_tmp; cin >> i_tmp; ret->data = i_tmp;//先读取第一个元素 Node* curNode = ret; Node_Stack.push(ret); while (--nn){//因为已经少一个了,所以--nn string type; cin >> type; if (type == "Push"){ int num_push; cin >> num_push; Node* newNode = new Node(num_push); if (curNode->lchild == NULL) curNode->lchild = newNode; else curNode->rchild = newNode; Node_Stack.push(newNode); curNode = newNode; } else if (type == "Pop"){ curNode = Node_Stack.top(); //*特别注意当前节点是pop出来的节点 Node_Stack.pop(); } } return ret; } void postOrder(Node* root){//后续遍历输出 if (root->lchild != NULL)postOrder(root->lchild); if (root->rchild != NULL)postOrder(root->rchild); static bool firstFlag = true;//设置标签位,看是否是第一次输出,为了最后的空格格式化,注意这里需要static if (firstFlag){ cout << root->data; firstFlag = false; } else cout << " " << root->data; } int main(){ freopen("F://Temp/input.txt", "r",stdin); int n; cin >> n; if (n == 0)return 0;//如果没有输入元素,则不用输出,直接返回 Node* root = createTree(2*n);//有2n组数据输入 postOrder(root); return 0; }
截图:
——Apie陈小旭
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