1020. Tree Traversals (25)

题目连接：https://www.patest.cn/contests/pat-a-practise/1020

原题如下：

Suppose that all the keys in a binary tree are distinct positive integers. Given the postorder and inorder traversal sequences, you are supposed to output the level order traversal sequence of the corresponding binary tree.

Input Specification:

Each input file contains one test case. For each case, the first line gives a positive integer N (<=30), the total number of nodes in the binary tree. The second line gives the postorder sequence and the third line gives the inorder sequence. All the numbers in a line are separated by a space.

Output Specification:

For each test case, print in one line the level order traversal sequence of the corresponding binary tree. All the numbers in a line must be separated by exactly one space, and there must be no extra space at the end of the line.

Sample Input:

7
2 3 1 5 7 6 4
1 2 3 4 5 6 7

Sample Output:

4 1 6 3 5 7 2
这道题是要求利用中序和后序写出层序。不用建树即可，利用递归。我写的还是有些繁琐了，主要是中间那块不太确定，求稳了些……
大致的思路就是先在后序中找到根，存入数组中，然后递归的解决左右两边，递归终止条件是参数中左边的序列大于右边。
代码如下：

#include<stdio.h>
#define MAXN 65535
int lastnum=0,N,PostOrder[MAXN],InOrder[MAXN];
int LevelOrder[MAXN]={0};

void Find(int Istart,int Iend,int Pstart,int Pend,int num)
{
    if (Iend<Istart||Pend<Pstart)return ;
    else
    {
        LevelOrder[num]=PostOrder[Pend];
       // printf("%d ",PostOrder[Pend]);
        if (num>lastnum)lastnum=num;
        int i;
        for (i=Istart;i<=Iend;i++)
        {
            if (InOrder[i]==PostOrder[Pend])break;
        }
        int center,Lchild,Rchild;
        int LengthLeft,LengthRight;
        int LeftEnd,RightEnd;

        center=i;

        LengthLeft=center-Istart;  //中序中的左边长度
        LengthRight=Iend-center;   //中序中的右边长度

        Lchild=num*2+1;  //左子树序号
        Rchild=num*2+2;  //右子树序号

        LeftEnd=Pstart+LengthLeft-1;  //后序中左半边的最右边界
        RightEnd=LeftEnd+LengthRight; //后序中右半边的最右边界

        Find(Istart,center-1,Pstart,LeftEnd,Lchild);
        Find(center+1,Iend,LeftEnd+1,RightEnd,Rchild);

    }
}
int main()
{
    int i;
    scanf("%d",&N);
    for (i=0;i<N;i++)scanf("%d",&PostOrder[i]);
    for (i=0;i<N;i++)scanf("%d",&InOrder[i]);

    Find(0,N-1,0,N-1,0);

    //printf("%d\n",lastnum);
    int flag=0;
    for (i=0;i<=lastnum;i++)
    {
        if (LevelOrder[i]!=0)
        {
           // printf("%d ",i);
            if (flag==0){printf("%d",LevelOrder[i]);flag=1;}
           else printf(" %d",LevelOrder[i]);
        }
    }

    return 0;
}