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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.
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:6Push 1Push 2Push 3PopPopPush 4PopPopPush 5Push 6PopPopSample Output:
3 4 2 6 5 1
#include#include #include #include #include #include #include using namespace std;struct Node{ int data; Node * left; Node * right; Node():data(0),left(NULL),right(NULL) {}; Node(int x):data(x),left(NULL),right(NULL) {};};void Post(Node *T,vector * o){ if(T->left) Post(T->left,o); if(T->right) Post(T->right,o); (*o).push_back(T->data);}int main(){ int n,num; cin>>n; string str; Node *lastpop=NULL,*root = NULL; stack sta; for(int i=0; i<2*n; ++i) { cin>>str; if(str=="Push") { cin>>num; if(sta.empty()&&lastpop==NULL) //上次没弹出,这次压入,根节点 { root = new Node(num); sta.push(root); } else if(lastpop) //上次有弹出,这次压入为右节点 { lastpop->right = new Node(num); sta.push(lastpop->right); } else//栈不为空且上次未弹出为压入栈顶元素左子树 { sta.top()->left = new Node(num); sta.push(sta.top()->left); } lastpop = NULL; } else { lastpop = sta.top(); sta.pop(); } } vector outt;//输出序列 Post(root,&outt); for_each(outt.begin(),outt.end(),[&](int a) { static int count = 0; cout<
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