[题目链接]
https://www.lydsy.com/JudgeOnline/problem.php?id=1660
[算法]
Sprease Table + 二分
时间复杂度 : O(NlogN)
[代码]
#include<bits/stdc++.h> using namespace std; #define MAXN 80010 #define MAXLOG 20 typedef long long ll; ll a[MAXN]; ll f[MAXN][MAXLOG]; template <typename T> inline void read(T &x) { ll f = 1; x = 0; char c = getchar(); for (; !isdigit(c); c = getchar()) { if (c == '-') f = -f; } for (; isdigit(c); c = getchar()) x = (x << 3) + (x << 1) + c - '0'; x *= f; } inline ll rmq(int x,int y) { int k = (int)(log(y - x + 1) / log(2.0)); return max(f[x][k],f[y - (1 << k) + 1][k]); } int main() { int n; read(n); for (int i = 1; i <= n; i++) read(a[i]); reverse(a + 1,a + n + 1); for (int i = 1; i <= n; i++) f[i][0] = a[i]; for (int i = 1; i < MAXLOG; i++) { for (int j = 1; j + (1 << i) - 1 <= n; j++) { f[j][i] = max(f[j][i - 1],f[j + (1 << (i - 1))][i - 1]); } } ll ans = 0; for (int i = 1; i <= n; i++) { int l = 1,r = i - 1,t = -1; while (l <= r) { int mid = (l + r) >> 1; if (rmq(mid,i - 1) < a[i]) { t = mid; r = mid - 1; } else l = mid + 1; } if (t != -1) ans += (ll)(i - t); } printf("%lld ",ans); return 0; }