Matrix Decompressing
题目:
给出一个矩阵的前i行,前j列的和。要求你求出满足的矩阵。
矩阵的数范围在[1,20]。
一開始就坑在了这里。没读细致题目。
囧。。。
事实上这题的模型就是一个网络流的行列模型,跟poj的那题budge一样建图。只是Poj 的那个建图输入麻烦。而这题是裸的,由于已经告诉你了下界为1,上界为20,囧。。。并且poj那题我至今也不知道为什么我会一直超时。
T_T
算法:
行列模型能够转换成网络流的有源汇上下界网络流求解。而行号和列号分别作为顶点。
连结超级源汇点就ok了。跑两边最大流,而每条边上的流量+下界流就是结果了。
#include <iostream>
#include <algorithm>
#include <vector>
#include <queue>
#include <cstdio>
#include <cstring>
using namespace std; const int INF = 1 << 20;
const int MAXN = 400 + 10;
struct Edge{
int from,to,cap,flow;
Edge(){};
Edge(int _from,int _to,int _cap,int _flow)
:from(_from),to(_to),cap(_cap),flow(_flow){};
};
vector<Edge> edges;
vector<int> G[MAXN];
int cur[MAXN],d[MAXN];
int N,M,src,sink,ss,tt; ////////////////////////////////////// int ans[MAXN][MAXN]; void init(){
ss = N + M + 2; tt = ss + 1;
src = tt + 1; sink = src + 1;
for(int i = 0;i <= sink + 1;++i)
G[i].clear();
edges.clear();
} void addEdge(int from,int to,int cap){
edges.push_back(Edge(from,to,cap,0));
edges.push_back(Edge(to,from,0,0));
int sz = edges.size();
G[from].push_back(sz - 2);
G[to].push_back(sz - 1);
} bool BFS(){
fill(d,d + sink + 2,-1);
queue<int> Q;
Q.push(src);
d[src] = 0; while(!Q.empty()){
int x = Q.front(); Q.pop();
for(int i = 0;i < (int)G[x].size();++i){
Edge& e = edges[G[x][i]];
if(d[e.to] == -1 && e.cap > e.flow){
d[e.to] = d[x] + 1;
Q.push(e.to);
}
}
} return d[sink] > 0;
} int DFS(int x,int a){
if(x == sink || a == 0)
return a; int flow = 0,f;
for(int& i = cur[x];i < (int)G[x].size();++i){
Edge& e = edges[G[x][i]];
if(d[e.to] == d[x] + 1 && (f = DFS(e.to,min(a,e.cap - e.flow))) > 0){
e.flow += f;
edges[G[x][i]^1].flow -= f;
flow += f;
a -= f;
if(a == 0) break;
}
}
return flow;
} int maxflow(){
int flow = 0;
while(BFS()){
memset(cur,0,sizeof(cur));
flow += DFS(src,INF);
}
return flow;
} int main()
{
// freopen("Input.txt","r",stdin); int T;
scanf("%d",&T);
for(int kase = 1;kase <= T;++kase){
scanf("%d%d",&N,&M); init(); int sum = 0,x;
for(int i = 1;i <= N;++i){
scanf("%d",&x);
addEdge(ss,i,x - sum);
sum = x;
} sum = 0;
for(int i = 1;i <= M;++i){
scanf("%d",&x);
addEdge(i+N,tt,x - sum);
sum = x;
} for(int i = 1;i <= N;++i){
for(int j = 1;j <= M;++j){
addEdge(i,sink,1);
addEdge(i,N + j,19);
addEdge(src,N + j,1);
}
} addEdge(tt,ss,INF); int flow = maxflow(); src = ss; sink = tt; maxflow();
printf("Matrix %d\n",kase); for(int i = 1;i <= N;++i){
for(int j = 0;j < (int)G[i].size();++j){
Edge& e = edges[G[i][j]];
if(e.from > N||e.to <= N||e.to > N+M) continue;
ans[e.from][e.to - N] = e.flow + 1;
}
} for(int i = 1;i <= N;++i){
for(int j = 1;j <= M;++j)
printf("%d%c",ans[i][j],j == M ? '\n':' ');
}
}
return 0;
}