poj 1459 push-relabel算法求最大流

 

#include <stdio.h>
#include <string.h>

#define DEBUG

#ifdef DEBUG
#define debug(...) printf( __VA_ARGS__) 
#else
#define debug(...)
#endif

#define N 102
#define MAX_INT 2000000

#define min(a, b) ((a) < (b) ? (a) : (b))

int		graph[N][N];
int		h[N];
int		e[N];
int		n;

int push_relabel(int s, int t)
{
	int 	max_flow, u, v, d, done, relabel, min_height;

	memset(h, 0, sizeof(h));
	memset(e, 0, sizeof(e));

	h[s] = n;
	for (u = 1; u <= t; u++) {
		if (graph[s][u] > 0) {
			e[u] = graph[s][u];
			e[s] -= graph[s][u];
			graph[u][s] = graph[s][u];
			graph[s][u] = 0;
		}
	}

	for (;;) {
		done = 1;
		for (u = s+1; u < t; u++) {
			if (e[u] > 0) {
				done = 0;
				//先假设顶点u需要relabel
				relabel = 1;
				for (v = s; v <= t && e[u] > 0; v++) {	/* 检查能push的顶点 */
					if (graph[u][v] > 0 && h[u] > h[v]) {
						//push
						relabel = 0;
						d = min(graph[u][v], e[u]);
						e[u] -= d;
						e[v] += d;
						graph[u][v] -= d;
						graph[v][u] += d;
						debug("push %d --%d--> %d, e[%d] = %d\n", u, d, u, u, e[u]);
					}
				}
				//没有可以push的顶点,执行relabel
				if (relabel) {
					//relabel
					min_height = MAX_INT;
					for (v = s; v <= t; v++) {
						if (graph[u][v] > 0 && h[v] < min_height) {
							min_height = h[v];
						}
					}
					h[u] = 1 + min_height;
					debug("relabel %d height to %d\n", u, h[u]);
				}
			}
		}
		if (done) {	/* 除源点和汇点外,每个顶点的e[i]都为0 */
			max_flow = 0;
			for (u = s; u <= t; u++) {
				if (graph[t][u] > 0) {
					max_flow += graph[t][u];
				}
			}
			break;
		}
	}
	return max_flow;
}

int main()
{
	int		np, nc, m, u, v, w;

	while (scanf("%d", &n) != EOF) {
		n += 2;		/* 添加源点和汇点 */
		scanf("%d %d %d", &np, &nc, &m);
		memset(graph, 0, sizeof(graph));
		//输入m条边
		while (m--) {
			scanf(" (%d,%d)%d", &u, &v, &w);
			graph[u+1][v+1] = w;
		}
		//输入np个power station
		while (np--) {
			scanf(" (%d)%d", &u, &w);
			graph[0][u+1] = w;
		}
		//输入nc个consumer
		while (nc--) {
			scanf(" (%d)%d", &u, &w);
			graph[u+1][n-1] = w;
		}
		printf("%d\n", push_relabel(0, n-1));
	}
	return 0;
}