1020. Tree Traversals (25)

the problem is from pat,which website is http://pat.zju.edu.cn/contests/pat-a-practise/1020

and the source code is as followed.

#include<iostream>

#include<cstdlib>

#include<queue>



using namespace std;



const int maxx = 32;



typedef struct Tree

{

    Tree *le;

    Tree *ri;

    int data;

}Tree;



Tree *root;



int pos[maxx],in[maxx];



void printLevelOrder(Tree *root)

{

    queue<Tree*> que;

    Tree *tr = NULL;

    que.push(root);

    bool flg = true;

    while (!que.empty())

    {

        tr = (Tree *)que.front();

        que.pop();

        if (tr == NULL) continue;

        if (flg)

        {

            printf("%d",tr->data);

            flg = false;

        }else

        {

            printf(" %d",tr->data);

        }

        que.push(tr->le);

        que.push(tr->ri);

    }

    printf("\n");

}



//构造树pl为后序序列的左边界pr为其右边界  

//il为中续遍历的左边界ir为其右边界 

Tree *buildTree(int pl,int pr,int il,int ir)

{

    if (pl > pr)return NULL;

    int p = il;

    while (in[p] != pos[pr])

    {

        ++p;

    }

    Tree *tree = (Tree *)malloc(sizeof(Tree));

    tree->data = pos[pr];

    tree->le = buildTree(pl,pr-ir+p-1,il,p-1);

    tree->ri = buildTree(pr-ir+p,pr-1,p+1,ir);  



    return tree; 

}



int main(){  

    int n,i;  

    Tree *root;  



    scanf("%d",&n);  

    for(i=0;i<n;++i){  

        scanf("%d",&pos[i]);  

    }  

    for(i=0;i<n;++i){  

        scanf("%d",&in[i]);  

    }  

    root=buildTree(0,n-1,0,n-1);  

    printLevelOrder(root);  

    return 0;  

}

the main function is rebuild the tree,which is a recursive function;and it is important to find

the left side and the right side from both postOrder and InOrder!Therefore ,we can use these argument to build the tree recursively.