HDU-1710-二叉树

#include <iostream>
using namespace std;

typedef long long ll;

const int maxn = 1010;

// 输入先序遍历和中序遍历， 求后序遍历；

int pre[maxn], in[maxn], post[maxn];
int k;

struct node
{
    int value;
    node *l, *r;
    node(int value = 0, node *l = nullptr, node *r = nullptr):
        value(value), l(l), r(r){}
};

void buildtree_dfs(int l, int r, int &t, node* &root)
{
    int flag = -1;
    for(int i = l; i <= r; i++)
    {
        if(in[i] == pre[t])
        {
            flag = i;
            break;
        }
    }
    if(flag == -1) return;
    root = new node(in[flag]);
    t++;
    if(flag > l) buildtree_dfs(l, flag - 1, t, root->l);
    if(flag < r) buildtree_dfs(flag + 1, r, t, root->r);
}

void preorder(node *root)
{
    if(root != nullptr)
    {
        post[k++] = root->value;
        preorder(root->l);
        preorder(root->r);
    }
}

void inorder(node *root)
{
    if(root != nullptr)
    {
        inorder(root->l);
        post[k++] = root->value;
        inorder(root->r);
    }
}

void postorder(node *root)
{
    if(root != nullptr)
    {
        postorder(root->l);
        postorder(root->r);
        post[k++] = root->value;
    }
}

int main()
{
    int n;
    while(cin >> n)
    {
        for(int i = 1; i <= n; i++) cin >> pre[i];
        for(int i = 1; i <= n; i++) cin >> in[i];
        node *root;
        int t = 1;
        buildtree_dfs(1, n, t, root);
        k = 0;
        postorder(root);
        for(int i = 0; i < k; i++)
        {
            cout << post[i];
            if(i != k - 1) cout << " ";
        }
        cout << endl;
    }
    return 0;
}