PAT1020

二叉树构建以及层次遍历

注意对递归边界的把握

之前的博客有错误，改正一下：

T->lchild = createBiTree(pos, in, index);
T->rchild = createBiTree(pos+index, in+index+1, len-index-1);

https://www.cnblogs.com/JCcodeblgos/p/11401423.html

#include <iostream>
#include <queue>

using namespace std;

const int maxn = 30+5;
string post_order[maxn], in_order[maxn], ans[maxn];

typedef struct BiTNode
{
    string data;
    struct BiTNode *lchild, *rchild;
}BiTNode, *BiTree;

BiTree createBiTree(string *pos, string *in, int len){
    // cout << pos << " " << in << " " << len << endl;
    if(len == 0)
        return NULL;
    
    string root = pos[len-1];
    int index = 0;
    while (in[index]!=root)
    {
        index++;
    }
    // cout << index << endl;
    BiTree T = new BiTNode;
    T->data = root;
    T->lchild = createBiTree(pos, in, index);
    T->rchild = createBiTree(pos+index, in+index+1, len-index-1);
    return T;
}

void leveltraverse(BiTree T){
    BiTree p;
    queue<BiTree> Q;
    Q.push(T);
    int index = 0;
    while (!Q.empty())
    {
        p = Q.front();
        Q.pop();
        ans[index++] =  p->data;
        if(p->lchild)
            Q.push(p->lchild);
        if(p->rchild)
            Q.push(p->rchild);
    }
}

int main(){
    // freopen("test.txt", "r", stdin);
    int n;
    cin >> n;
    for(int i=0; i<n; i++)
        cin >> post_order[i];
    for(int i=0; i<n; i++)
        cin >> in_order[i];
//    for(int i=0; i<n; i++)
//        cout << post_order[i] << " ";
//    cout << endl;
//    for(int i=0; i<n; i++)
//        cout << in_order[i] << " ";
//    cout << endl;
    BiTree T = createBiTree(post_order, in_order, n);
    leveltraverse(T);
    for(int i=0; i<n; i++){
        if(i != 0)
            cout << " ";
        cout << ans[i];
    }
}