HDU 3549 Flow Problem 最大流 最小增广路 SAP算法 从EK算法的753MS降到了46MS

EK 算法的链接：http://blog.csdn.net/ipqhjjybj/article/details/9171181

SAP算法果然对这个优化了好多。。时间直接从753MS降到46MS呀。。

题目描述

Network flow is a well-known difficult problem for ACMers. Given a graph, your task is to find out the maximum flow for the weighted directed graph.

Input:

The first line of input contains an integer T, denoting the number of test cases.
For each test case, the first line contains two integers N and M, denoting the number of vertexes and edges in the graph. (2 <= N <= 15, 0 <= M <= 1000)
Next M lines, each line contains three integers X, Y and C, there is an edge from X to Y and the capacity of it is C. (1 <= X, Y <= N, 1 <= C <= 1000)

#include <cstdio>#include <cmath>#include <cstdlib>#include <ctime>#include <iostream>#include <cmath>#include <algorithm>#include <numeric>#include <utility>#include <cstring>#include <vector>#include <stack>#include <queue>#include <map>#include <string>using namespace std;#define inf 0x3f3f3f3f#define MAXN 20#define MAXM 1005#define clr(x,k) memset((x),(k),sizeof(x))#define cpy(x,k) memcpy((x),(k),sizeof(x))#define Base 10000typedef vector<int> vi;typedef stack<int> si;typedef vector<string> vs;#define sz(a) int((a).size())#define pb push_back#define all(c) (c).begin(),(c).end()#define rep(i,n) for(int i = 0;i < n;++i)#define foreach(it,c) for(vi::iterator it = (c).begin();it != (c).end();++it)#define max(a,b) ((a)>(b)?(a):(b))#define min(a,b) ((a)<(b)?(a):(b))struct node{    int c,next,to;}edges[MAXM];int box[MAXN],n,m,tot;void add(int a,int b,int c){    edges[tot].to=b;    edges[tot].c=c;    edges[tot].next=box[a];    box[a]=tot++;}int Map[MAXN][MAXN]; //map:邻接数组 因为可能有重边情况。优化下，再用SAP算法void init(){    clr(Map,0);    for(int i = 0,a,b,c;i < m;i++){        scanf("%d %d %d",&a,&b,&c);        Map[a][b] += c;    }    tot=2;    clr(box,-1);    for(int i = 1;i <= n;i++)        for(int j = 1;j <= n;j++)            if(Map[i][j])                add(i,j,Map[i][j]),add(j,i,0);}int SAP_Max_Flow(int start,int end,int N){    int numh[MAXN],h[MAXN],curedges[MAXN],pre[MAXN];    //numh: 用于GAP优化的统计高度数量数组；h:距离标号数组;curedges;当前弧数组,pre,前驱数组    int cur_flow,flow_ans=0,u,tmp,neck,i;    clr(h,0);    clr(numh,0);    clr(pre,-1);    for(i = 1;i <= n;i++)        curedges[i]=box[i];    numh[0]=N;    u=start;    while(h[start]<N){        if(u==end){            cur_flow=inf;            for(i=start;i!=end;i=edges[curedges[i]].to){                if(cur_flow>edges[curedges[i]].c){                    neck=i;                    cur_flow=edges[curedges[i]].c;                }            }            for(i=start;i!=end;i=edges[curedges[i]].to){                tmp=curedges[i];                edges[tmp].c-=cur_flow;                edges[tmp^1].c+=cur_flow;            }            flow_ans+=cur_flow;            u=neck;        }        for(i=curedges[u];i!=-1;i=edges[i].next){            if(edges[i].c&&h[u]==h[edges[i].to]+1)                break;        }        if(i!=-1){            curedges[u]=i;            pre[edges[i].to]=u;            u=edges[i].to;        }        else{            if(0==--numh[h[u]])break;            curedges[u]=box[u];            for(tmp=N,i=box[u];i!=-1;i=edges[i].next)                if(edges[i].c)                    tmp=min(tmp,h[edges[i].to]);            h[u]=tmp+1;            ++numh[h[u]];            if(u!=start) u=pre[u];        }    }    return flow_ans;}int main(){    //freopen("3549.in","r",stdin);    int t,tt=0;    scanf("%d",&t);    while(t--){        scanf("%d %d",&n,&m);        init();        printf("Case %d: %d\n",++tt,SAP_Max_Flow(1,n,n));    }    return 0;}