第K大区间

51NOD 1686
中文题
这题很坑。。。。区间众数是从大开始依次减小的排在一起，然后去找。。。一开始理解反了。。。

主要是利用二分和尺取法去求，题目给的数比较大，一开始先离散化，然后每次二分一个值，利用尺取法判断大于等于mid的区间是否超过k个。
因为是从大开始排列，所以不需要用n*(n-1)/2-res;而是直接是res…..

#include <algorithm>#include <iostream>#include <cstring>#include <cstdlib>#include <vector>#include <cstdio>#include <bitset>#include <cmath>#include <queue>#include <stack>#include <map>#include <set>#define FOR(i,a,b) for(int i=a;i<=b;i++)#define ROF(i,a,b) for(int i=a;i>=b;i--)#define mem(i,a) memset(i,a,sizeof(i))#define rson mid+1,r,rt<<1|1#define lson l,mid,rt<<1#define mp make_pair#define pb push_back#define ll long long#define LL long longusing namespace std;template <typename T>inline void read(T &_x_){    _x_=0;bool f=false;char ch=getchar();    while (ch<'0'||ch>'9') {if (ch=='-') f=!f;ch=getchar();}    while ('0'<=ch&&ch<='9') {_x_=_x_*10+ch-'0';ch=getchar();}    if(f) _x_=-_x_;}const double eps = 1e-8;const int maxn = 2e5+7;const int mod = 1e9+7;const ll inf = 1e15;ll n,m;ll a[maxn],b[maxn];ll cnt[maxn];bool check(ll mid){    mem(cnt,0);    ll l=1,r=1;    ll res=0;    while(r<=n){        cnt[a[r]]++;        while(cnt[a[r]]>=mid){            res+=n-r+1;            cnt[a[l]]--;            l++;        }        if(res>=m) return true;        r++;    }    return false;}int main(){    read(n),read(m);    FOR(i,1,n) read(a[i]),b[i]=a[i];    sort(b+1,b+1+n);    int pos = unique(b+1,b+1+n)-b;    FOR(i,1,n) a[i] = lower_bound(b+1,b+1+pos,a[i])-b;    ll l=0,r=n*(n-1)/2,mid;    while(l+1<r){        mid=(l+r)/2;        if(check(mid)) l=mid;        else r = mid;    }    printf("%I64d\n",l);    return 0;}