AtCoder Beginner Contest 320 Problem D - Relative Position 题解

题目保证不矛盾，就可以直接 vector 建图，然后 dfs 一遍，边权为 \((w_x,w_y)\) 表示坐标的差，从 \(u=1\) 开始搜索，设点 \(u,v\) 有一条无向边，\(v_x = u_x + w_x,v_y = u_y + w_y\)，最后如果没有被标记过的话（也就是没有遍历过），那么无解。

AC Code

#include<iostream>
#include<vector>

using namespace std;

const int MAXN = 2e5 + 10;

struct node{
    int t, x, y;
};

struct ANS{
    long long a, b;
}ans[MAXN];

vector<node> G[MAXN];
int n, m, a, b, x, y;
bool vis[MAXN];

void dfs(int u, long long x, long long y){
    if (vis[u]){
        return;
    }
    vis[u] = 1,ans[u] = {x, y};
    for (int i = 0; i < G[u].size(); i++){
        dfs(G[u][i].t, x + G[u][i].x, y + G[u][i].y);
    }
}

int main(){
    cin >> n >> m;
    for (int i = 1; i <= m; i++){
        cin >> a >> b >> x >> y;
        G[a].push_back({b, x, y}), G[b].push_back({a, -x, -y});
    }
    dfs(1, 0, 0);
    for (int i = 1; i <= n; i++){
        if (!vis[i]){
            cout << "undecidable\n";
        }
        else {
            cout << ans[i].a << ' ' << ans[i].b << '\n';
        }
    }
    return 0;
}