BZOJ1930 [Shoi2003]pacman eats peas

Shoi had such a ghost problem? Kneeling

First, we can think of the cost of network flow, find a flow of 2 of the maximum cost flow can be, the question is how to build a map

Because the point is to gain, and only once the proceeds, so consider the split, it may be possible to set a point P split into points P1 and out point P2

Then P1-P2 with the edge flow of 1, the cost is 1, and then the edge traffic is 1, the cost is 0;s to P1 with the edge of 1, the cost is 0;p2 to the t edge, the flow is 1, the cost is 0

If p can reach Q, then P2-Q1 with a flow of 2, the cost is 0

Then you will find too many sides ... Optimization?

If I can reach the j,j can reach K, then I do not to the K-side, so it is a monotone problem, the point of the x-axis sorting, and then the y-axis monotonically increased in the way of the edge.

1 /**************************************************************2 problem:19303 User:rausen4 language:c++5 result:accepted6 time:192 Ms7 memory:63416 KB8 ****************************************************************/9  Ten#include <cstdio> One#include <algorithm> A   - using namespacestd; - Const intN = -; the Const intM = 4e6 +5; - Const intINF =1e9; -   -InlineintRead () { +     intx =0; -     CharCH =GetChar (); +      while(Ch <'0'||'9'<ch) ACH =GetChar (); at      while('0'<= CH && Ch <='9') { -x = x *Ten+ CH-'0'; -CH =GetChar (); -     } -     returnx; - } in   - structPoint { to     intx, y; +       -Inlinevoidread_in () { thex = Read (), y =read (); *     } $InlineBOOL operator< (ConstPoint &p)Const {Panax Notoginseng         returnx = = p.x? Y < P.y:x <p.x; -     } the } P[n]; +   A structEdges { the     intnext, to, F, cost; + edges () {} -Edgesint_n,int_t,int_f,int_c): Next (_n), to (_t), F (_f), cost (_c) {} $ } E[m]; $   - intN, S, S1, T; - intFirst[n <<1], tot =1; the intA[n]; - intD[n <<1], G[n <<1], Q[n <<1], Vis[n <<1];Wuyi BOOLV[n <<1]; the   -InlinevoidAdd_edges (intXintYintFintc) { WuE[++tot] = Edges (first[x], y, F, c), first[x] =tot; -E[++tot] = Edges (First[y], X,0,-C), first[y] =tot; About } $    -InlineintCalc () { -     intFlow =inf, x; -      for(x = g[t]; x = g[e[x ^1].to]) AFlow =min (flow, e[x].f); +      for(x = g[t]; x = g[e[x ^1].to]) theE[X].F-= flow, e[x ^1].F + =flow; -     returnflow; $ } the   the #defineY e[x].to the BOOLSPFA () { the     intx, now, L, R; -      for(x =1; x <= S1; ++x) inD[X] =inf; theD[s] =0, v[s] =1, q[0] =S; the      for(L = r =0; L! = (R +1) %N;) { Aboutnow = Q[l], ++l%=N; the          for(x = First[now]; x; x =E[x].next) { the             if(D[now] + e[x].cost < D[y] &&e[x].f) { theD[y] = D[now] + e[x].cost, g[y] =x; +                 if(!V[y]) { -V[y] =1; the                     if(D[y] <D[q[l]])Bayiq[(L + = N-1)%= N] =y; the                     ElseQ[++r%= N] =y; the                 } -             } -         } theV[now] =0; the     } the     returnD[T]! =inf; the } - #undefY the   theInlineintWork () { the     intres =0;94      while(SPFA ()) theRes + = Calc () *D[t]; the     returnRes; the }98   About #defineP1 (i) (I << 1)-1 - #defineP2 (i) (I << 1)101 intMain () {102     intI, J, TMP;103n = Read (), S = n *2+1, T = S +1, S1 = T +1;104      for(i =1; I <= N; ++i) the p[i].read_in ();106Sort (p +1, p + n +1);107      for(i =1; I <= N; ++i) {108A[i] = P[I].Y, TMP =-1;109Add_edges (S1, p1 (i),1,0), Add_edges (P2 (i), T,1,0); theAdd_edges (P1 (i), p2 (i),1, -1), Add_edges (P1 (i), p2 (i),1,0);111          for(j = i-1; J --j) the             if(A[j] <= a[i] && A[j] >tmp)113TMP = A[j], Add_edges (P2 (j), p1 (i),2,0); the     } theAdd_edges (S, S1,2,0); theprintf"%d\n", -Work ());117     return 0;118}

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BZOJ1930 [Shoi2003]pacman eats peas