UVa563 - Crimewave

/***********************************************
最大流算法(dinic)
在深搜时，刚开始没有把d[cur] = -1超时，改之后就好了
相当于一个剪枝操作
***********************************************/
#include <iostream>
#include <queue>
#include <cstring>
#include <fstream>
#include <cstdio>using namespace std;const int MAXD = 7200;
const int MAXM = 36000;
const int INF = 1000000000;int first[MAXD], next[MAXM], u[MAXM], v[MAXM], flow[MAXM];
int d[MAXD];
int s, a, b;
int e;void init();
void add(int x, int y, int f);
int bfs();
int dfs(int cur, int f);
int dinic();int main(int argc, char *argv[])
{int t;#ifndef ONLINE_JUDGEfreopen("d:\\OJ\\uva_in.txt", "r", stdin);
#endif // ONLINE_JUDGEscanf("%d", &t);while (t--) {init();int ans = dinic();if (ans)printf("possible\n");elseprintf("not possible\n");}return 0;
}void init()
{e = 0;//cin >> s >> a >> b;scanf("%d%d%d", &s, &a, &b);memset(first, -1, sizeof(first));memset(flow, 0, sizeof(flow));for (int i = 1; i <= a; i++) {int z = a + i;add(2 * z ^ 1, 1, 1);add(1, 2 * z ^ 1, 0);}for (int i = 1; i <= s; i++) {int z = i * a + 1;add(2 * z ^ 1, 1, 1);add(1, 2 * z ^ 1, 0);}for (int i = 1; i <= a; i++) {int z = s * a + i;add(2 * z ^ 1, 1, 1);add(1, 2 * z ^ 1, 0);}for (int i = 1; i <= s; i++) {int z = i * a + a;add(2 * z ^ 1, 1, 1);add(1, 2 * z ^ 1, 0);}for (int i = 1; i <= s; i++) {for (int j = 1; j <= a; j++) {int z = i * a + j;add(2 * z, 2 * z ^ 1, 1);add(2 * z ^ 1, 2 * z, 0);if (i + 1 <= s) {int newz = (i + 1) * a + j;add(2 * z ^ 1, 2 * newz, 1);add(2 * newz, 2 * z ^ 1, 0);add(2 * newz ^ 1, 2 * z, 1);add(2 * z, 2 * newz ^ 1, 0);}if (j + 1 <= a) {int newz = i * a + j + 1;add(2 * z ^ 1, 2 * newz, 1);add(2 * newz, 2 * z ^ 1, 0);add(2 * newz ^ 1, 2 * z, 1);add(2 * z, 2 * newz ^ 1, 0);}}}for (int i = 0; i < b; i++) {int x, y, z;scanf("%d%d", &x, &y);z = x * a + y;add(0, 2 * z, 1);add(2 * z, 0, 0);}}void add(int x, int y, int f)
{u[e] = x;v[e] = y;flow[e] = f;next[e] = first[x];first[x] = e;e++;
}int bfs()
{queue<int> q;memset(d, -1, sizeof(d));q.push(0);d[0] = 0;while (!q.empty()) {int u1 = q.front();q.pop();for (int j = first[u1]; j != -1; j = next[j]) {if (flow[j] > 0 && d[v[j]] == -1) {d[v[j]] = d[u1] + 1;if (v[j] == 1)return 1;q.push(v[j]);}}}return 0;
}int dfs(int cur, int f)
{if (cur == 1 || f == 0)return f;int ans = 0;for (int j = first[cur]; j != -1; j = next[j]) {if (flow[j] > 0 && d[v[j]] == d[cur] + 1) {int t = dfs(v[j], flow[j] < f ? flow[j]:f);flow[j] -= t;flow[j ^ 1] += t;f -= t;ans += t;if (f == 0) break;}}d[cur] = -1;return ans;
}int dinic()
{int ans = 0;while (bfs()) {ans += dfs(0, INF);}if (ans == b)return 1;else return 0;
}

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