通过前序(后序)+中序创建树

Posted 2020-11-10 TheQi

通过二叉树的前序遍历和中序遍历创建树

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
typedef struct NODE
{
    int nValue;
    struct NODE* pLeft;
    struct NODE* pRight;
}BinaryTree;

int Getxb(char* inorder,int num)
{
    //得到根在中序遍历中的下标
    for(int i=0;i<strlen(inorder);i++)
    {
        if(inorder[i] == num)
            return i;
    }
    return -1;
}
BinaryTree* CreateNode(char c)
{
    BinaryTree* ptemp = (BinaryTree*)malloc(sizeof(BinaryTree));
    ptemp->nValue = c;
    ptemp->pLeft = NULL;
    ptemp->pRight = NULL;

    return ptemp;
}
BinaryTree* CreateTree(char* pre,char* in)
{
    if(pre == NULL || in == NULL) return NULL;
    if(*pre == NULL) return NULL;
    char szPreorder[100];
    char szInorder[100];
    memset(szPreorder,0,100);
    memset(szInorder,0,100);

    BinaryTree* pNode = CreateNode(pre[0]);

    int index = Getxb(in,pre[0]);
    //index等于几代表根有几个左
    strncpy(szPreorder,pre+1,index);
    strncpy(szInorder,in,index);
    pNode->pLeft = CreateTree(szPreorder,szInorder);

    memset(szPreorder,0,100);
    memset(szInorder,0,100);
    //右的数量等于strlen-左-根(1)
    strncpy(szPreorder,pre+1+index,strlen(pre)-index-1);
    strncpy(szInorder,in+1+index,strlen(pre)-index-1);
    pNode->pRight = CreateTree(szPreorder,szInorder);

    return pNode;

}

void Preorder(BinaryTree* pNode)
{
    if(pNode == NULL) return;
    Preorder(pNode->pLeft);
    Preorder(pNode->pRight);
    printf("%d ",pNode->nValue-48);

}

int main()
{
    char szbuf1[10];
    char szbuf2[10];
    BinaryTree* p = CreateTree("124536","425163");
    Preorder(p);
    return 0;
}

通过二叉树的后序遍历和中序遍历创建树

只有创建树的代码换了

BinaryTree* CreateTree(char* post,char* in)
{
    if(post == NULL || in == NULL) return NULL;
    if(*post == NULL) return NULL;
    //根节点在后序遍历的最后
    int num = strlen(post)-1;
    char szInorder[100];
    char szPostorder[100];
    memset(szInorder,0,100);
    memset(szPostorder,0,100);

    BinaryTree* pTree = CreateNode(post[num]);
    //得到中序遍历中根的下标,index代表根有几个左
    int index = Getxb(in,post[num]);
    strncpy(szInorder,in,index);
    strncpy(szPostorder,post,index);
    pTree->pLeft = CreateTree(szPostorder,szInorder);

    memset(szInorder,0,100);
    memset(szPostorder,0,100);
    //右的数量等于strlen-左-根(1)
    strncpy(szInorder,in+1+index,strlen(in)-1-index);
    strncpy(szPostorder,post+index,strlen(in)-1-index);
    pTree->pRight = CreateTree(szPostorder,szInorder);
    return pTree;
}