[随机 Hash] Codeforces 799F Round #413 F. Beautiful fountains rows

就是给题目中给出的每个区间随一个值 然后判断一个区间是否合法 把区间内所有数xor和 再xor上 区间中出现过的所有数的xor和 为 0
前缀和统计下
本人脸黑 单hash交了好几发都是WA 迫不得已双hash

#include<cstdio>#include<cstdlib>#include<algorithm>#include<vector>#include<map>#include<ctime>#define pb push_back using namespace std;typedef unsigned long long ull;typedef long long ll;typedef pair<ull,ull> abcd;inline ll sum(ll n){ return n*(n+1)/2;}inline ll sum2(ll n){ return n*(n+1)*(2*n+1)/6;}inline ll calc(ll n){ return (n+1)*sum(n)-sum2(n);}const int N=200005;#define read(x) scanf("%d",&(x))int n,m;int l[N],r[N];vector<int> L[N],R[N];ull h1[N],h2[N],a[N],b[N];map<abcd,ll> F,G;ll ans;int cnt[N];int main(){  srand(time(0));  freopen("t.in","r",stdin);  freopen("t.out","w",stdout);  read(n); read(m);  for (int i=1;i<=n;i++){    read(l[i]); read(r[i]);    L[l[i]].pb(i); R[r[i]].pb(i);    a[i]=(ull)rand()*rand()*rand()*rand()*rand();    b[i]=(ull)rand()*rand()*rand()*rand()*rand();    h1[l[i]]^=a[i]; h1[r[i]+1]^=a[i];    h2[l[i]]^=b[i]; h2[r[i]+1]^=b[i];    cnt[l[i]]++; cnt[r[i]+1]--;  }  for (int i=1;i<=m;i++) h1[i]^=h1[i-1],h2[i]^=h2[i-1];  for (int i=1;i<=m;i++) h1[i]^=h1[i-1],h2[i]^=h2[i-1];  G[abcd(0,0)]++; F[abcd(0,0)]=0;  ull s1=0,s2=0,t1=0,t2=0;  for (int i=1;i<=m;i++){    for (int x:L[i]) s1^=a[x],s2^=b[x];    ans+=G[abcd(s1^h1[i],s2^h2[i])]*i-F[abcd(s1^h1[i],s2^h2[i])];    for (int x:R[i]) t1^=a[x],t2^=b[x];    F[abcd(t1^h1[i],t2^h2[i])]+=i; G[abcd(t1^h1[i],t2^h2[i])]++;  }  for (int i=1;i<=m;i++) cnt[i]+=cnt[i-1];  for (int i=1;i<=m;)    if (cnt[i]==0){      int j=i; while (j+1<=m && cnt[j+1]==0) j++;      ans-=calc(j-i+1);      i=j+1;    }else      i++;  printf("%I64d\n",ans);  return 0;}