PAT天梯赛题目集：Level2-006.树的遍历-优快云博客

本文介绍了一种通过后序遍历和中序遍历构建二叉树，并进一步实现层序遍历的方法。该算法使用了递归方式解决从给定的后序和中序遍历序列构建出完整的二叉树并进行层次遍历的问题。

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题： https://www.patest.cn/contests/gplt/L2-006

#include <iostream>
#include <vector>
using std::cin;
using std::cout;
std::vector<int> PostOrder_Traversal, InOrder_Traversal;
std::vector<int> &post = PostOrder_Traversal, &in = InOrder_Traversal;
std::vector<int> LevelOrder_Traversal(10000, -1), &level = LevelOrder_Traversal;
void solve(int start, int end, int root, int index) {
    if (start > end)
        return;
    int i = start;
    while (i < end && in[i] != post[root])
        i++;
    level.at(index) = post.at(root);
    solve(start, i - 1, root - (end - i) - 1, 2 * index + 1);
    solve(i + 1, end, root - 1, 2 * index + 2);
}
int main() {
    std::ios::sync_with_stdio(false);
    cin.tie(false);

    int TreeNode_Num;
    int &N = TreeNode_Num;
    int cnt = 0;
    cin >> N;
    post.resize(N);
    in.resize(N);
    for (int i = 0; i < N; ++i)
        cin >> post[i];
    for (int i = 0; i < N; ++i)
        cin >> in[i];
    solve(0, N - 1, N - 1, 0);
    for (int i = 0; i < level.size(); ++i) {
        if (level.at(i) != -1 && cnt++ != N - 1) 
            cout << level.at(i) << ' ';
        else if (level.at(i) != -1) {
            cout << level.at(i);
            break;
        }
    }
    return 0;
}