L2-006 树的遍历

先建树，再BFS

#include <bits/stdc++.h>

using namespace std;

vector<int> tree[35];

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n;
    cin >> n;
    vector<int> postorder(n);
    vector<int> inorder(n);
   
    map<int, int> posorderId;
    map<int, int> inorderId;
    for (int i = 0; i < n; i++) {
        cin >> postorder[i];
        posorderId[postorder[i]] = i;
    }
    for (int i = 0; i < n; i++) {
        cin >> inorder[i];
        inorderId[inorder[i]] = i;
    }

    function<void(int, int, int)> build = [&](int l, int r, int mid) {
        if (l > r) return;
        //找左子树的根
        int lroot = -1;
        for (int i = l; i <= mid - 1; i++) {
            int u = inorder[i];
            if (lroot == -1 || posorderId[u] > posorderId[lroot]) {
                lroot = u;
            }
        }

        //找右子树的根
        int rroot = -1;
        for (int i = mid + 1; i <= r; i++) {
            int u = inorder[i];
            if (rroot == -1 || posorderId[u] > posorderId[rroot]) {
                rroot = u;
            }
        }

        tree[inorder[mid]].push_back(lroot), tree[inorder[mid]].push_back(rroot);

        if (lroot != -1) build(l, mid - 1, inorderId[lroot]);
        if (rroot != -1)build(mid + 1, r, inorderId[rroot]);
    };

    build(0, n - 1, inorderId[postorder.back()]);
    
    vector<int> leTravel;
    function<void (int)> levelTravel = [&](int u) {
        queue<int> q;
        q.push(u);
        leTravel.push_back(u);
        while (q.size()) {
            int t = q.front(); q.pop();
            for (auto &itr : tree[t]) {
                if (itr == -1) continue;
                leTravel.push_back(itr);
                q.push(itr);
            }
        }
    };
    
    levelTravel(postorder.back());
    
    for (int i = 0; i < leTravel.size(); i++) {
        cout << leTravel[i] << " "[i == leTravel.size() - 1];
    }

    return 0;
}
//4.16
//4.8
//