[hdu5400 Arithmetic Sequence]预处理,容斥
2015-08-18 23:00
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题意:http://acm.hdu.edu.cn/showproblem.php?pid=5400
思路:预处理出每个点向左和向右的最远边界,从左向右枚举中间点,把区间答案加到总答案里面。由与可能与前面的区间重叠,需要减去重复的答案,由于左边界非降,所以重叠的区间长度很容易得到。
思路:预处理出每个点向左和向右的最远边界,从左向右枚举中间点,把区间答案加到总答案里面。由与可能与前面的区间重叠,需要减去重复的答案,由于左边界非降,所以重叠的区间长度很容易得到。
#pragma comment(linker, "/STACK:10240000") #include <map> #include <set> #include <cmath> #include <ctime> #include <deque> #include <queue> #include <stack> #include <vector> #include <cstdio> #include <string> #include <cstdlib> #include <cstring> #include <iostream> #include <algorithm> using namespace std; #define X first #define Y second #define pb push_back #define mp make_pair #define all(a) (a).begin(), (a).end() #define fillchar(a, x) memset(a, x, sizeof(a)) #define copy(a, b) memcpy(a, b, sizeof(a)) typedef long long ll; typedef pair<int, int> pii; typedef unsigned long long ull; //#ifndef ONLINE_JUDGE void RI(vector<int>&a,int n){a.resize(n);for(int i=0;i<n;i++)scanf("%d",&a[i]);} void RI(){}void RI(int&X){scanf("%d",&X);}template<typename...R> void RI(int&f,R&...r){RI(f);RI(r...);}void RI(int*p,int*q){int d=p<q?1:-1; while(p!=q){scanf("%d",p);p+=d;}}void print(){cout<<endl;}template<typename T> void print(const T t){cout<<t<<endl;}template<typename F,typename...R> void print(const F f,const R...r){cout<<f<<", ";print(r...);}template<typename T> void print(T*p, T*q){int d=p<q?1:-1;while(p!=q){cout<<*p<<", ";p+=d;}cout<<endl;} //#endif template<typename T>bool umax(T&a, const T&b){return b<=a?false:(a=b,true);} template<typename T>bool umin(T&a, const T&b){return b>=a?false:(a=b,true);} const double PI = acos(-1.0); const int INF = 1e9 + 7; const double EPS = 1e-12; /* -------------------------------------------------------------------------------- */ const int maxn = 1e5 + 7; int a[maxn], R[maxn], L[maxn]; int main() { #ifndef ONLINE_JUDGE freopen("in.txt", "r", stdin); //freopen("out.txt", "w", stdout); #endif // ONLINE_JUDGE int n, d1, d2; while (cin >> n >> d1 >> d2) { for (int i = 1; i <= n; i ++) { scanf("%d", a + i); } for (int i = n; i >= 2; i --) { a[i] = a[i] - a[i - 1]; } a[n + 1] = INF * 2; R[n + 1] = INF; for (int i = 1; i <= n; i ++) { L[i] = max(1, a[i] == d1? L[i - 1] : i); } for (int i = n; i; i --) { R[i] = min(n, a[i + 1] == d2? R[i + 1] : i); } int lastl = 0, lastr =0; ll ans = 0; for (int i = 1; i <= n; i ++) { ll c = R[i] - L[i] + 1; ans += c * (c + 1) / 2; ll cc = min(lastr, R[i]) - L[i] + 1; if (cc > 0) ans -= cc * (cc + 1) / 2; lastl = L[i]; umax(lastr, R[i]); } cout << ans << endl; } return 0; }
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