codeforces 190D Non-Secret Cypher 双指针

给定长度为n的数组a，给定k，问有多少个子数组，其中至少包含着有k个相同的数字

双指针经典题目，注意先要离散，然后注意m是1的情况

#include <iostream>
#include <cstring>
#include <cstdio>
#include <algorithm>
#include <map>
#define rep(i, j, k) for(int i = j; i <= k; i++)
#define maxn 1000009
#define ll long long

using namespace std;

int n, m, a[maxn], c[maxn], now = 0, cnt = 0;
int cunt[maxn];
map <int, int> mp;
ll ans = 0;

int main ()
{
cin >> n >> m;
rep (i, 1, n)
cin >> a[i], c[i] = a[i];
sort (c + 1, c + 1 + n);
c[0] = c[1] - 1;
cnt = 0;
rep (i, 1, n)
if (c[i] != c[i - 1])
mp[c[i]] = ++cnt;
rep (i, 1, n)
a[i] = mp[a[i]];
//rep (i, 1, n) printf ("%d %d\n", i, a[i]);
int r = 1;
cunt[a[1]]++;
if (m == 1)
now++;
rep (l, 1, n)
{
while (now == 0 && r < n)
{
r++;
cunt[a[r]]++;
if (cunt[a[r]] >= m)
now++;
}
if (now)
ans += 1LL * n - 1LL * r + 1LL;
cunt[a[l]]--;
if (cunt[a[l]] == m - 1)
now--;
}
cout << ans << endl;
}