[题目链接]
http://poj.org/problem?id=3422
[算法]
费用流
[代码]
#include <algorithm> #include <bitset> #include <cctype> #include <cerrno> #include <clocale> #include <cmath> #include <complex> #include <cstdio> #include <cstdlib> #include <cstring> #include <ctime> #include <deque> #include <exception> #include <fstream> #include <functional> #include <limits> #include <list> #include <map> #include <iomanip> #include <ios> #include <iosfwd> #include <iostream> #include <istream> #include <ostream> #include <queue> #include <set> #include <sstream> #include <stdexcept> #include <streambuf> #include <string> #include <utility> #include <vector> #include <cwchar> #include <cwctype> #include <stack> #include <limits.h> using namespace std; #define MAXN 310 const int inf = 2e9; struct edge { int to,w,cost,nxt; } e[MAXN * MAXN * 8]; int i,j,n,k,tot,val,ans,S,T; int head[MAXN * MAXN * 2],dist[MAXN * MAXN * 2],incf[MAXN * MAXN * 2],pre[MAXN * MAXN * 2]; inline int id(int x,int y,int k) { return (x - 1) * n + y + n * n * k; } inline void addedge(int u,int v,int w,int cost) { tot++; e[tot] = (edge){v,w,cost,head[u]}; head[u] = tot; tot++; e[tot] = (edge){u,0,-cost,head[v]}; head[v] = tot; } inline bool spfa() { int i,u,v,w,cost,l,r; static int q[MAXN * MAXN * 2]; static bool inq[MAXN * MAXN * 2]; for (i = 1; i <= T; i++) { dist[i] = -inf; incf[i] = inf; } memset(inq,false,sizeof(inq)); inq[S] = true; pre[S] = 0; dist[S] = 0; incf[S] = inf; q[l = r = 1] = S; while (l <= r) { u = q[l]; l++; inq[u] = false; for (i = head[u]; i; i = e[i].nxt) { v = e[i].to; w = e[i].w; cost = e[i].cost; if (w && dist[u] + cost > dist[v]) { dist[v] = dist[u] + cost; incf[v] = min(incf[u],w); pre[v] = i; if (!inq[v]) { inq[v] = true; q[++r] = v; } } } } if (dist[T] != -inf) return true; else return false; } inline void update() { int x = T,pos; while (x != S) { pos = pre[x]; e[pos].w -= incf[T]; e[pos ^ 1].w += incf[T]; x = e[pos ^ 1].to; } ans += dist[T] * incf[T]; } int main() { scanf("%d%d",&n,&k); tot = 1; for (i = 1; i <= n; i++) { for (j = 1; j <= n; j++) { scanf("%d",&val); addedge(id(i,j,0),id(i,j,1),1,val); addedge(id(i,j,0),id(i,j,1),k - 1,0); if (i < n) addedge(id(i,j,1),id(i + 1,j,0),k,0); if (j < n) addedge(id(i,j,1),id(i,j + 1,0),k,0); } } S = 1; T = 2 * n * n; while (spfa()) update(); printf("%d ",ans); return 0; }