hdu 1565 方格取數(1)【最大流】
阿新 • • 發佈:2019-01-26
程式碼:
#include <iostream>
#include <algorithm>
#include <set>
#include <map>
#include <string.h>
#include <queue>
#include <sstream>
#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#include <string>
using namespace std;
const int MAXN = 1010000;//點數的最大值
const int MAXM = 6001000;//邊數的最大值
const int INF = 0x3f3f3f3f;
struct Edge
{
int to, next, cap, flow;
}edge[MAXM];//注意是MAXM
int tol;
int head[MAXN];
int gap[MAXN], dep[MAXN], pre[MAXN], cur[MAXN];
void init()
{
tol = 0;
memset(head, -1, sizeof(head));
}
//加邊,單向圖三個引數,雙向圖四個引數
void addedge(int u, int v, int w, int rw = 0)
{
edge[tol].to = v; edge[tol].cap = w; edge[tol].next = head[u];
edge[tol].flow = 0; head[u] = tol++;
edge[tol].to = u; edge[tol].cap = rw; edge[tol].next = head[v];
edge[tol].flow = 0; head[v] = tol++;
}
//輸入引數:起點、終點、點的總數
//點的編號沒有影響,只要輸入點的總數
int Q[MAXN];
void BFS(int start,int end)
{
memset(dep, -1, sizeof(dep));
memset(gap, 0, sizeof(gap));
gap[0] = 1;
int front = 0, rear = 0;
dep[end] = 0;
Q[rear++] = end;
while (front != rear)
{
int u = Q[front++];
for (int i = head[u];i != -1;i = edge[i].next)
{
int v = edge[i].to;
if (dep[v] != -1) continue;
Q[rear++] = v;
dep[v] = dep[u] + 1;
gap[dep[v]]++;
}
}
}
int S[MAXN];
int sap(int start, int end, int N)
{
BFS(start, end);
memcpy(cur, head, sizeof(head));
int u = start;
int top = 0;
int ans = 0;
while (dep[start] < N)
{
if (u == end)
{
int Min = INF;
int inser;
for (int i = 0; i < top; i++)
if (Min > edge[S[i]].cap - edge[S[i]].flow)
{
Min = edge[S[i]].cap - edge[S[i]].flow;
inser = i;
}
for (int i = 0; i < top; i++)
{
edge[S[i]].flow += Min;
edge[S[i] ^ 1].flow -= Min;
}
ans += Min;
top = inser;
u = edge[S[top] ^ 1].to;
continue;
}
bool flag = false;
int v;
for (int i = cur[u]; i != -1; i = edge[i].next)
{
v = edge[i].to;
if (edge[i].cap - edge[i].flow && dep[v] + 1 == dep[u])
{
flag = true;
cur[u] = i;
break;
}
}
if (flag)
{
S[top++] = cur[u];
u = v;
continue;
}
int Min = N;
for (int i = head[u]; i != -1; i = edge[i].next)
if (edge[i].cap - edge[i].flow && dep[edge[i].to] < Min)
{
Min = dep[edge[i].to];
cur[u] = i;
}
gap[dep[u]]--;
if (!gap[dep[u]])return ans;
dep[u] = Min + 1;
gap[dep[u]]++;
if (u != start) u = edge[S[--top]^1].to;
}
return ans;
}
int n, m;
int a[110][110];
int dir[4][2] = {{1,0},{-1,0},{0,1},{0,-1}};
int main()
{
while(scanf("%d",&n)!=EOF)
{
m = n;
int sum = 0;
init();
for(int i=1;i<=n;i++)
for(int j=1;j<=m;j++)
{
scanf("%d",&a[i][j]);
sum += a[i][j];
if ((i+j) % 2 == 0)
{
addedge(0,(i-1)*m+j,a[i][j]);
}
else
{
addedge((i-1)*m+j,n*m+1,a[i][j]);
}
}
for(int i=1;i<=n;i++)
for(int j=1;j<=m;j++)
{
if ((i + j) % 2 == 0)
for(int k=0;k<4;k++)
{
int x = i + dir[k][0];
int y = j + dir[k][1];
if (x>=1 && x<= n &&y>=1 && y<=m)
{
addedge((i-1)*m+j,(x-1)*m+y,1e9+9);
}
}
}
int ans = sum - sap(0,n*m + 1,n*m + 2);
printf("%d\n",ans);
}
return 0;
}