关于二叉树的问题1-已知前序，中序求后序遍历

对于一棵二叉树而言，可以由其前序和中序或者中序和后序的遍历序列，确定一棵二叉树。

那么对于已知前序和中序序列，求后序序列也就是先还原二叉树，然后对其进行后序遍历即可。

二叉树结点的结构定义如下:

struct TreeNode
{
    char value;
    TreeNode *leftChild;
    TreeNode *rightChild;
};

实现代码如下：

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

TreeNode* allocateNode()
{

    TreeNode* node = (TreeNode*)malloc(sizeof(TreeNode));
    node->leftChild = nullptr;
    node->rightChild = nullptr;
    return node;
}

char preStr[50], inStr[50];
void postOrder(TreeNode *T)
{
    if (T->leftChild != nullptr)
    {
        postOrder(T->leftChild);
    }
    if (T->rightChild != nullptr)
    {
        postOrder(T->rightChild);
    }
    printf("%c ", T->value);
}

TreeNode* builtTree(int start1, int end1, int start2, int end2)
{
    TreeNode *node = allocateNode();
    node->value = preStr[start1];
    int nodeIndex;
    for (int i = start2; i <= end2; ++i)
    if (preStr[start1] == inStr[i])
    {
        nodeIndex = i;
        break;
    }
    if (nodeIndex != start2)
    {
        node->leftChild = builtTree(start1 + 1, start1 + (nodeIndex - start2), start2, nodeIndex - 1);
    }

    if (nodeIndex != end2)
    {
        node->rightChild = builtTree(start1 + (nodeIndex - start2) + 1, end1, nodeIndex + 1, end2);
    }
    return node;
}

void main(void)
{
    scanf("%s",preStr);
    scanf("%s", inStr);
    int preLen = strlen(preStr);
    int inLen = strlen(inStr);
    TreeNode *root = builtTree(0, preLen - 1, 0, inLen - 1);
    postOrder(root);

}