【HDOJ】2732 Leapin' Lizards

贪心+网络流。对于每个结点，构建入点和出点。
对于每一个lizard>0,构建边s->in position of lizard， 容量为1.
对于pillar>0, 构建边in position of pillar -> out position of pillar, 容量为number of pillar.
若沿四个方向移动距离d可以超过边界，则构建边out position of pillar -> t， 容量为INF；
否则， 对于曼哈顿距离l(l>0 and l<=d)的点p构建边out position of pillar -> in position p, 容量为INF。（此时，不用考虑p是否含有pillar，无所谓）
Dinic可解网络流。一定要注意输出was/were，单复数和0等。

  1 /* 2732 */
  2 #include <iostream>
  3 #include <string>
  4 #include <map>
  5 #include <queue>
  6 #include <set>
  7 #include <stack>
  8 #include <vector>
  9 #include <deque>
 10 #include <algorithm>
 11 #include <cstdio>
 12 #include <cmath>
 13 #include <ctime>
 14 #include <cstring>
 15 #include <climits>
 16 #include <cctype>
 17 #include <cassert>
 18 #include <functional>
 19 #include <iterator>
 20 #include <iomanip>
 21 using namespace std;
 22 //#pragma comment(linker,"/STACK:102400000,1024000")
 23
 24 #define sti                set<int>
 25 #define stpii            set<pair<int, int> >
 26 #define mpii            map<int,int>
 27 #define vi                vector<int>
 28 #define pii                pair<int,int>
 29 #define vpii            vector<pair<int,int> >
 30 #define rep(i, a, n)     for (int i=a;i<n;++i)
 31 #define per(i, a, n)     for (int i=n-1;i>=a;--i)
 32 #define clr                clear
 33 #define pb                 push_back
 34 #define mp                 make_pair
 35 #define fir                first
 36 #define sec                second
 37 #define all(x)             (x).begin(),(x).end()
 38 #define SZ(x)             ((int)(x).size())
 39 #define lson            l, mid, rt<<1
 40 #define rson            mid+1, r, rt<<1|1
 41
 42 const int INF = 0x1f1f1f1f;
 43 const int maxn = 25;
 44 const int maxv = maxn*maxn*2;
 45 const int maxe = maxv*maxn*8;
 46 int V[maxe], F[maxe], nxt[maxe];
 47 int head[maxv], dis[maxv];
 48 char Ps[maxn][maxn], Ls[maxn][maxn];
 49 int dir[4][2] = {
 50     -1, 0, 1, 0, 0, -1, 0, 1
 51 };
 52 int n, m;
 53
 54 void addEdge(int u, int v, int c) {
 55     V[m] = v;
 56     F[m] = c;
 57     nxt[m] = head[u];
 58     head[u] = m++;
 59
 60     V[m] = u;
 61     F[m] = 0;
 62     nxt[m] = head[v];
 63     head[v] = m++;
 64 }
 65
 66 bool bfs(int s, int t) {
 67     queue<int> Q;
 68     int u, v, k;
 69
 70     memset(dis, 0, sizeof(dis));
 71     Q.push(s);
 72     dis[s] = 1;
 73
 74     while (!Q.empty()) {
 75         u = Q.front();
 76         Q.pop();
 77         for (k=head[u]; k!=-1; k=nxt[k]) {
 78             v = V[k];
 79             if (!dis[v] && F[k]) {
 80                 dis[v] = dis[u] + 1;
 81                 Q.push(v);
 82             }
 83         }
 84     }
 85
 86     return dis[t]==0;
 87 }
 88
 89 int dfs(int u, int t, int val) {
 90     if (u==t || val==0)
 91         return val;
 92
 93     int ret = 0;
 94     int tmp, v, k;
 95
 96     for (k=head[u]; k!=-1; k=nxt[k]) {
 97         v = V[k];
 98         if (dis[v]==dis[u]+1 && F[k] && (tmp=dfs(v, t, min(val, F[k])))>0) {
 99             F[k] -= tmp;
100             F[k^1] += tmp;
101             ret += tmp;
102             val -= tmp;
103             if (val == 0)
104                 break;
105         }
106     }
107
108     return ret;
109 }
110
111 int Dinic(int s, int t) {
112     int ret = 0, tmp;
113
114     while (1) {
115         if (bfs(s, t))
116             break;
117
118         tmp = dfs(s, t, INF);
119         ret += tmp;
120     }
121
122     return ret;
123 }
124
125 int main() {
126     ios::sync_with_stdio(false);
127     #ifndef ONLINE_JUDGE
128         freopen("data.in", "r", stdin);
129         freopen("data.out", "w", stdout);
130     #endif
131
132     int case_n;
133     int s, t, n_, m_, d, tmp;
134     int x, y;
135     int k, id, id_;
136     int ans, tot;
137     bool flag;
138
139     scanf("%d", &case_n);
140     rep(tt, 1, case_n+1) {
141         scanf("%d %d", &n_, &d);
142
143         rep(i, 1, n_+1)
144             scanf("%s", Ps[i]+1);
145         rep(i, 1, n_+1)
146             scanf("%s", Ls[i]+1);
147
148         m_ = strlen(Ps[1]+1);
149         tot = 0;
150         s = m = 0;
151         k = n_ * m_;
152         t = k*2+1;
153         memset(head, -1, sizeof(head));
154
155         rep(i, 1, n_+1) {
156             rep(j, 1, m_+1) {
157                 id = (i-1) * m_ + j;
158                 if (Ls[i][j] == ‘L‘) {
159                     addEdge(s, id, 1);
160                     ++tot;
161                 }
162                 if (Ps[i][j] > ‘0‘) {
163                     addEdge(id, id+k, Ps[i][j]-‘0‘);
164                     flag = true;
165                     id += k;
166                     rep(kk, 0, 4) {
167                         x = i + dir[kk][0] * d;
168                         y = j + dir[kk][1] * d;
169                         if (x<=0 || x>n_ || y<=0 || y>m_) {
170                             addEdge(id, t, INF);
171                             flag = false;
172                             break;
173                         }
174                     }
175                     if (flag) {
176                         id_ = 0;
177                         rep(ii, 1, n_+1) {
178                             rep(jj, 1, m_+1) {
179                                 ++id_;
180                                 tmp = abs(ii-i) + abs(jj-j);
181                                 if (tmp>0 && tmp<=d)
182                                     addEdge(id, id_, Ps[i][j]-‘0‘);
183                             }
184                         }
185                     }
186                 }
187             }
188         }
189
190         ans = tot - Dinic(s, t);
191         printf("Case #%d: ", tt);
192         if (ans == 0) {
193             printf("no lizard was left behind.\n");
194         } else if (ans == 1) {
195             printf("1 lizard was left behind.\n");
196         } else {
197             printf("%d lizards were left behind.\n", ans);
198         }
199     }
200
201     #ifndef ONLINE_JUDGE
202         printf("time = %d.\n", (int)clock());
203     #endif
204
205     return 0;
206 }

【HDOJ】2732 Leapin' Lizards