Hdu3549--flow Problem (maximum flow (EK algorithm | | ISAP optimization) _ACM Competition

Topic Source: http://showproblem.php?pid=3549

A network is given to maximize the flow 、。。。 Ideas

There seems to be no idea, the template,,,
Brush three water problems, and finally can go to learn isap ... (Good food ...) Want to cry no tears form ... ) code

#include <cmath> #include <stack> #include <queue> #include <cstdio> #include <cstring> #
Include<algorithm> using namespace std;
const int MAXN=19+10;
const int inf=0x3f3f3f3f;
int n,m;
int PRE[MAXN],F_L[MAXN][MAXN];
BOOL VIS[MAXN];
    void Init () {scanf ("%d%d", &n,&m);
    memset (f_l,0,sizeof (f_l));
        while (m--) {int x,y,w;
        scanf ("%d%d%d", &x,&y,&w);
    F_l[x][y]+=w;
    } bool BFs () {memset (vis,0,sizeof (VIS));
    memset (pre,-1,sizeof (pre));
    Queue<int> Q;
    Q.push (1);
    Vis[1]=1; while (!
        Q.empty ()) {int U=q.front ();
        Q.pop ();
                for (int v=1; v<=n; v++) {if (!vis[v]&&f_l[u][v)) {pre[v]=u;
                Vis[v]=1;
                if (v==n) return 1;
            Q.push (v);
}} return 0;
    } void Print_ek () {int maxflow=0; while (BFS ()) {int tt=n,minN=inf;
            while (tt!=1) {minn=min (F_l[pre[tt]][tt],minn);
        TT=PRE[TT];
        } Maxflow+=minn;
        Tt=n;
            while (tt!=1) {F_l[pre[tt]][tt]-=minn;
            F_l[tt][pre[tt]]+=minn;
        TT=PRE[TT];
} printf ("%d\n", Maxflow);
    int main () {int T;
    scanf ("%d", &t);
        for (int i=1;i<=t;i++) {init ();
        printf ("Case%d:", i);
    Print_ek ();
return 0;

 }

ISAP optimization #include <cstdio> #include <cstring> #include <queue> #include <algorithm> using
namespace Std;
const int inf=0x3f3f3f3f;
const int MAXN=1000+10;
Use elevation, look for the path, and put the edge of the ordinal record in the array, found, to operate.
    struct PP {int v,nexx;
int flow,cap;
}edge[maxn<<1];
int FIRST[MAXN],H[MAXN],NUM[MAXN],CUR[MAXN],S[MAXN];
ISAP: adjacency table + array record int n,m,tot;
    void ADD (int u,int v,int W) {edge[tot].v=v;
    edge[tot].flow=0;
    Edge[tot].cap=w;
    Edge[tot].nexx=first[u];
first[u]=tot++;
    } void init (int i) {tot=0;
    scanf ("%d%d", &n,&m);
    memset (First,-1,sizeof (a));
        while (m--) {int u,v,w;
        scanf ("%d%d%d", &u,&v,&w);
        ADD (U,V,W);
    ADD (v,u,0);
printf ("Case%d:", i);}
    void height () {queue<int> Q; while (!
    Q.empty ()) Q.pop ();
    memset (h,-1,sizeof (h));
    memset (num,0,sizeof (num));
    Q.push (n);
    h[n]=0;
    ++NUM[0]; while (!
        Q.empty ()) {int U=q.front (); Q.poP ();
            for (int i=first[u];i!=-1;i=edge[i].nexx) {int v=edge[i].v;
                if (h[v]==-1) {h[v]=h[u]+1;
                Q.push (v);
            num[h[v]]++;
    }} void Print_isap (int s,int t) {height ();
    int ans=0,top=0,u=s;
    memcpy (Cur,first,sizeof (a));
            while (h[s]<n) {if (u==t) {int d=inf,pos;
                    for (int i=0;i<top;i++) {if (D>edge[s[i]].cap-edge[s[i]].flow) {
                    D=edge[s[i]].cap-edge[s[i]].flow;
                Pos=i;
                } for (int i=0;i<top;i++) {edge[s[i]].flow+=d;
            Edge[s[i]^1].flow-=d;
            } Top=pos;
            Ans+=d;
        u=edge[s[top]^1].v;//back point continue; The int i=cur[u];//starts with the next for (; I!=-1;i=edge[i].nexx) {
            if (edge[i].cap>edge[i].flow&&h[u]==h[edge[i].v]+1) {cur[u]=i;
                S[top++]=i;
                U=EDGE[I].V;
            Break } if (i==-1) {int d=n;//fallback, mark height for (int I=first[u];i!=-1;i=edge[i].nex
                    x) {if (edge[i].cap>edge[i].flow&&d>h[edge[i].v]) {
                    D=H[EDGE[I].V];
                Cur[u]=i; } if (--num[h[u]]==0) break;//If there is only one point at the current height, the fault will occur after the change.
            Exit ++num[h[u]=d+1];
if (u!=s) u=edge[s[--top]^1].v;//back to previous} printf ("%d\n", ans);
    int main () {int T;
    scanf ("%d", &t);
        for (int i=1;i<=t;i++) {init (i);
    PRINT_ISAP (1,n);
 }
}