数据结构

前序和中序构造二叉树

前序和中序、后序和中序序列可以构造唯一一颗二叉树.
1.从前序序列找到父节点,即首个结点;
2.中序序列找到此父结点,它的左右分别对应左孩子和右孩子;
以此递归,直到满足边界值.

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#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<stack>
#include<queue>
using namespace std;

typedef char DATA_TYPE;

typedef struct node
{
    DATA_TYPE data;
    node *lch, *rch;
    node()
    {
        lch = rch = 0;
    }
} Node;

void print(Node *r)
{
    if(r)
    {
        print(r->lch);
        printf("%c", r->data);
        print(r->rch);
        free(r);
    }
}

Node *buildTree(char *pre, int idxStart, int idxEnd, char *mid, int idxS, int idxE)
{
    if(idxStart==idxEnd || idxS >= idxE) return NULL;
    int i = idxS;
    Node *node = (Node*)malloc(sizeof(Node));
    node->data=pre[idxStart];
    node->lch=node->rch=NULL;
    for(; i<idxE; i++)
    {
        if(pre[idxStart] == mid[i])break;
    }

    if(i==idxEnd)
    {
        return buildTree(pre, idxStart+1, idxEnd, mid, idxS, idxE);
    }
    else
    {
        node->lch = buildTree(pre, idxStart+1, idxEnd, mid, idxS, i);
        node->rch = buildTree(pre, idxStart+1, idxEnd, mid, i+1, idxE);
    }
    return node;
}

int main()
{
    DATA_TYPE preOrderTraversal[] = "abdejcfig";
    DATA_TYPE inOrderTraversal[] = "dbjeaficg";
    Node *root = buildTree(preOrderTraversal, 0, 9, inOrderTraversal, 0, 9);
    print(root);
    return 0;
}