CF - 741(C. Arpa’s overnight party and Mehrdad’s silent entering) 二分图构造

题目链接

题意

已经给出情侣的座位编号,将两种饭分配给N对情侣.满足以下两个要求:

情侣之间不能吃相同的饭
座位号连续的三个人不能吃同一种饭

问是否存在满足的解.

思路

构造二分图

对应情侣的座位建边,保证情侣之间不吃一种饭
[2i-1, 2i]建边,保证座位号相邻的3个人不全吃一种饭

#include <bits/stdc++.h>
const int maxn = 2e5 + 5;
const int inf = 0x3f3f3f3f;
const int mod = 1e9 + 7;
using namespace std;
vector<int> g[maxn];
void add(int u, int v) {g[u].push_back(v); g[v].push_back(u);
}
int color[maxn], flag;
void dfs(int u, int col) {color[u] = col;for (int i = 0; i < (int)g[u].size(); ++i) {int v = g[u][i];if (color[v] == -1) dfs(v, col^1);else if (color[v] == col) flag = -1;}
}
vector<pair<int,int>> all;
int main() {ios::sync_with_stdio(0);cin.tie(0), cout.tie(0);int n;scanf("%d", &n);for (int i = 1, u, v; i <= n; ++i) {add(i*2-1, i*2);scanf("%d %d", &u, &v);all.push_back(make_pair(u, v));add(u, v);}fill(color, color+maxn, -1);flag = 1;for (int i = 1; i <= n*2; ++i) {if (color[i] == -1) dfs(i, 0);}if (flag == -1) puts("-1");else {for (auto it : all) {printf("%d %d\n", color[it.first]+1, color[it.second]+1);}}return 0;
}

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CF - 741(C. Arpa’s overnight party and Mehrdad’s silent entering) 二分图构造

题意

思路

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