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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.
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： 主要是根据输入创建一个二叉树，然后进行后续遍历
代码：
#pragma mark -Tree Traversals Again #include <stdio.h> typedef struct traversalTreeNode { int value; struct traversalTreeNode *left; struct traversalTreeNode *right; } TraversalTreeNode; int flag; TraversalTreeNode *createTraversalTreeNode(int value) { TraversalTreeNode *node = (TraversalTreeNode *)malloc(sizeof(TraversalTreeNode)); node->value = value; node->left = NULL; node->right = NULL; return node; } void postorderTraversal(TraversalTreeNode *head) { if (head) { postorderTraversal(head->left); postorderTraversal(head->right); if (flag == 0) { printf("%d", head->value); flag = 1; } else { printf(" %d", head->value); } } } int main() { int nodeNum = 0; scanf("%d", &nodeNum); int operationCount = 2 * nodeNum; TraversalTreeNode *a[30]; int top = -1; // 第一个节点肯定是PUSH int index = -1; scanf("%*s %d", &index); TraversalTreeNode *head = createTraversalTreeNode(index); a[0] = head; top = 0; TraversalTreeNode *popItem = NULL; for (int i = 1; i < operationCount; i++) { int index = -1; char str[4]; scanf("%s", str); unsigned long len = strlen(str); if (len >= 4) { scanf("%d", &index); TraversalTreeNode *newNode = createTraversalTreeNode(index); if (popItem) { if (!popItem->left) { popItem->left = newNode; } else { popItem->right = newNode; } } else { if (!a[top]->left) { a[top]->left = newNode; } else { a[top]->right = newNode; } } top++; a[top] = newNode; popItem = NULL; } else { popItem = a[top]; a[top] = NULL; top--; } } flag = 0; postorderTraversal(head); }
运行结果：
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原文地址：http://www.cnblogs.com/liufeng24/p/4419588.html
