dinic算法 c 语言,ACM/ICPC 之 Dinic算法（POJ2112）

//二分枚举最大距离的最小值+Floyd找到最短路+Dinic算法

//参考图论算法书，并对BFS构建层次网络算法进行改进

//Time:157Ms Memory:652K

#include

#include

#include

#include

#include

using namespace std;

#define MAX 250

#define INF 0x3f3f3f3f

int K, C, M;

int s, t;

int d[MAX][MAX];//各点间最短距离

int res[MAX][MAX];//残留网络

int lev[MAX];

void build_map(int limit)

{

memset(res,0,sizeof(res));

for (int i = K + 1; i <= K + C; i++)

res[s][i] = 1;

for (int i = 1; i <= K; i++)

res[i][t] = M;

for (int i = K + 1; i <= K + C; i++)

for (int j = 1; j <= K; j++)

if (d[i][j] <= limit)res[i][j] = 1;

}

bool bfs() //BFS标记层次网络

{

memset(lev, -1, sizeof(lev));

queue q;

q.push(s);

lev[s] = 0;

while (!q.empty()) { //构建层次网络

int cur = q.front();

q.pop();

for(int i = 1; i <= t; i++)

{

if(lev[i] == -1 && res[cur][i]) //未访问且正向有流量

{

q.push(i);

lev[i] = lev[cur] + 1;

}

}

}

return lev[t] != -1;

}

int dfs(int v, int alpha) //DFS进行多次增广

{

if(v == t || alpha == 0) return alpha;

int src = alpha; //原可改进量

for(int i = 1; i <= t; i++)

{

if(res[v][i] && lev[i] == lev[v] + 1){ //识别下一层次

int tmp = dfs(i, min(alpha, res[v][i]));

res[v][i] -= tmp;

res[i][v] += tmp;

alpha -= tmp; //可改进量减少

}

}

return src - alpha; //总改进量

}

int main()

{

//freopen("in.txt", "r", stdin);

scanf("%d%d%d", &K,&C,&M);

s = 0; t = K + C + 1; //源点-汇点

for (int i = 1; i < t; i++)

for (int j = 1; j < t; j++)

{

scanf("%d", &d[i][j]);

if (d[i][j] == 0)d[i][j] = INF;

}

for (int k = 1; k < t; k++)

for (int i = 1; i < t; i++)

{

if (d[i][k] != INF) {

for (int j = 1; j < t; j++)

d[i][j] = min(d[i][j], d[i][k] + d[k][j]);

}

}

s = 0;t = K + C + 1;//源点 汇点

int l = 0, r = 9000;

while (l < r)

{

int ans = 0; //到达目的地的奶牛数量

int mid = (l + r) / 2;

build_map(mid);

while (bfs())

ans += dfs(0,INF); //第二参数指定该点可改进量

ans == C ? r = mid: l = mid+1;

}

printf("%d

", r);

return 0;

}