Bzoj 3175: [Tjoi2013] Attack device (Hungary)

Black and white dyed into a binary chart, and then can not be selected at the same time, the maximum number of matches m, T is the number can not be put, then the topic of the maximum point independent set of N*N-M-T

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#include <cstdio>#include <cstring>#include <algorithm>using namespace std;const int MAXN = 209;const int Dir[8][2] = {{-1,-2}, {-2,-1}, {1,-2},{2,-1}, {-1, 2}, {-2, 1},{1, 2}, {2, 1}};struct Edge {int to;edge* Next;} E[MAXN * MAXN * 8], *pt = E, *HEAD[MAXN * MAXN];void Addedge (int u, int v) {pt->to = v; pt->next = head[u]; Head[u] = pt++;}Char STR[MAXN][MAXN];int N, VIS[MAXN * MAXN], C, MATCH[MAXN * MAXN], ans;int Id (int x, int y) {return x * N + y;}bool Dfs (int x) {For (edge* e = head[x]; e; e = e->next) if (vis[e->to]! = C) {vis[e->to] = C;if (!~match[e->to] | | DFS (MATCH[E->TO)) {match[e->to] = x;return true;}}return false;}bool Checky (int x, int y) {return (x + y) & 1;}void init () {scanf ("%d", &n);ans = n * n;for (int i = 0; i < N; i++) scanf ("%s", Str[i]);for (int i = 0; i < N; i++) {For (int j = 0; J < N; J + +) if (str[i][j] = = ' 0 ') {int id = ID (i, j);if (!checky (i, J)) {for (int k = 0; k < 8; k++) {int x = i + dir[k][0], y = j + dir[k][1];if (x >= 0 && x < N && y >= 0 && y < N && str[x][y] = = ' 0 ' && check Y (x, y))Addedge (ID, id (x, y));}}} elseans--;}}void Work () {memset (Match,-1, sizeof match);memset (Vis,-1, sizeof vis);int lim = n * N;For (C = 0; C < Lim; C + +) if (Dfs (C)) ans--;printf ("%d\n", ans);}int main () {init ();Work ();return 0;}

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3175: [Tjoi2013] Attack device Time Limit:Ten Sec Memory Limit:MB
Submit:754 Solved:362
[Submit] [Status] [Discuss] Description

Given a 01 matrix, where you can place the attack device in 0 locations. Each attack device (x, y) can be attacked by the word "day" in 8 locations (x-1,y-2), (x-2,y-1), (x+1,y-2), (x+2,y-1), (x-1,y+2), (x-2,y+1), (x+1,y+2), (x+2,y+1)
The maximum number of devices that can be placed in the case of non-attack by the device.

Input The first line is an integer N, which indicates that the matrix size is n*n. Next n rows each row a length of N of 01 strings, representing the matrix. Output An integer that represents the maximum number of devices that can be placed if the device is not attacking. Sample Input 3
010
000
100
Sample Output 4HINT

100% Data n<=200

Source

Bzoj 3175: [Tjoi2013] Attack device (Hungary)