• poj2987 Firing


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    基础建图 最大权闭合子图

    有点像依赖背包

    看到的时候就知道是最小割

    建图;

    1.正点向源点,负点向汇点连点权绝对值的边

    2.原图中的单向边不变,流量为inf

    这样一来图里最小割就是所有人都用上之后(源点没有出去的边)花掉的钱

    就拿所有正点权的点权和减最小割就行

    注意开ll...

    Code:

      1 #include<cstdio>
      2 #include<cstring>
      3 #include<queue>
      4 #include<iostream>
      5 #include<algorithm>
      6 #define ms(a,b) memset(a,b,sizeof a)
      7 #define rep(i,a,n) for(int i = a;i <= n;i++)
      8 #define per(i,n,a) for(int i = n;i >= a;i--)
      9 #define inf 2147483647
     10 using namespace std;
     11 typedef long long ll;
     12 typedef double D;
     13 #define eps 1e-8
     14 ll read() {
     15     ll as = 0,fu = 1;
     16     char c = getchar();
     17     while(c < '0' || c > '9') {
     18         if(c == '-') fu = -1;
     19         c = getchar();
     20     }
     21     while(c >= '0' && c <= '9') {
     22         as = as * 10 + c - '0';
     23         c = getchar();
     24     }
     25     return as * fu;
     26 }
     27 const int N = 5005;
     28 const int M = 180005;
     29 //head
     30 int s = N-2,t = N-1;
     31 int head[N],nxt[M],mo[M],cnt = 1;
     32 ll cst[M];
     33 void _add(int x,int y,ll w) {
     34     mo[++cnt] = y;
     35     cst[cnt] = w;
     36     nxt[cnt] = head[x];
     37     head[x] = cnt;
     38 }
     39 void add(int x,int y,ll w) {
     40     if(x^y) _add(x,y,w),_add(y,x,0);
     41 }
     42 
     43 int dep[N],cur[N];
     44 bool bfs() {
     45     queue<int> q;
     46     memcpy(cur,head,sizeof cur);
     47     ms(dep,0),q.push(s),dep[s] = 1;
     48     while(!q.empty()) {
     49         int x = q.front();
     50         q.pop();
     51         for(int i = head[x];i;i = nxt[i]) {
     52             int sn = mo[i];
     53             if(!dep[sn] && cst[i]) {
     54                 dep[sn] = dep[x] + 1;
     55                 q.push(sn);
     56             }
     57         }
     58     }
     59     return (bool)dep[t];
     60 }
     61 
     62 ll dfs(int x,ll flow) {
     63     if(x == t || flow == 0ll) return flow;
     64     ll res = 0;
     65     for(int &i = cur[x];i;i = nxt[i]) {
     66         int sn = mo[i];
     67         if(dep[sn] == dep[x] + 1 && cst[i]) {
     68             ll d = dfs(sn,min(cst[i],flow - res));
     69             if(d) {
     70                 cst[i] -= d,cst[i^1] += d;
     71                 res += d;
     72                 if(res == flow) break;
     73             }
     74         }
     75     }
     76     if(res ^ flow) dep[x] = 0;
     77     return res;
     78 }
     79 
     80 ll DINIC() {
     81     ll ans = 0;
     82     while(bfs()) ans += dfs(s,inf);
     83     return ans;
     84 }
     85 
     86 
     87 bool vis[N];
     88 void dfs(int x) {
     89     vis[x] = 1;
     90     for(int i = head[x];i;i = nxt[i]) {
     91         int sn = mo[i];
     92         if(!vis[sn] && cst[i]) dfs(sn);
     93     }
     94 }
     95 
     96 int n,m;
     97 ll sum,ans;
     98 void solve() {
     99     ms(vis,0),ms(head,0),cnt = 1,ans = sum = 0ll;
    100     rep(i,1,n) {
    101         ll x = read();
    102         if(x > 0) add(s,i,x),ans += x;
    103         if(x < 0) add(i,t,-x);
    104     }
    105     rep(i,1,m) {
    106         int x = read(),y = read();
    107         add(x,y,inf);
    108     }
    109     ans -= DINIC();
    110     dfs(s);
    111     rep(i,1,n) sum += vis[i];
    112     printf("%lld %lld
    ",sum,ans);
    113 }
    114 
    115 
    116 int main(){while(~scanf("%d%d",&n,&m)) solve();}
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  • 原文地址:https://www.cnblogs.com/yuyanjiaB/p/10011827.html
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