Codeforces 1167E Range Deleting

Range Deleting

考虑枚举L, R明显具有可二分性， 然后预处理一些东西， 二分就好啦。

#include<bits/stdc++.h>
#define LL long long
#define LD long double
#define ull unsigned long long
#define fi first
#define se second
#define mk make_pair
#define PLL pair<LL, LL>
#define PLI pair<LL, int>
#define PII pair<int, int>
#define SZ(x) ((int)x.size())
#define ALL(x) (x).begin(), (x).end()
#define fio ios::sync_with_stdio(false); cin.tie(0);

using namespace std;

const int N = 1e6 + 7;
const int inf = 0x3f3f3f3f;
const LL INF = 0x3f3f3f3f3f3f3f3f;
const int mod = 1e9 + 7;
const double eps = 1e-8;
const double PI = acos(-1);

template<class T, class S> inline void add(T& a, S b) {a += b; if(a >= mod) a -= mod;}
template<class T, class S> inline void sub(T& a, S b) {a -= b; if(a < 0) a += mod;}
template<class T, class S> inline bool chkmax(T& a, S b) {return a < b ? a = b, true : false;}
template<class T, class S> inline bool chkmin(T& a, S b) {return a > b ? a = b, true : false;}

int n, x, a[N];
int mnPos[N], mxPos[N];
int preMax[N], sufMin[N];
bool preCan[N], sufCan[N];

inline bool check(int l, int r) {
    if(!preCan[l - 1]) return false;
    if(!sufCan[r + 1]) return false;
    if(sufMin[r + 1] < preMax[l - 1]) return false;
    return true;
}

int main() {
    memset(mnPos, inf, sizeof(mnPos));
    scanf("%d%d", &n, &x);
    sufMin[x + 1] = inf;
    preMax[0] = -inf;
    for(int i = 1; i <= n; i++) scanf("%d", &a[i]);
    for(int i = 1; i <= n; i++) {
        chkmax(mxPos[a[i]], i);
        chkmin(mnPos[a[i]], i);
    }
    preMax[1] = mxPos[1];
    for(int i = 2; i <= x; i++) preMax[i] = max(preMax[i - 1], mxPos[i]);
    sufMin[x] = mnPos[x];
    for(int i = x - 1; i >= 1; i--) sufMin[i] = min(sufMin[i + 1], mnPos[i]);
    preCan[0] = true;
    for(int i = 1; i <= x; i++) {
        if(!preCan[i - 1]) break;
        if(mnPos[i] > preMax[i - 1]) preCan[i] = true;
    }
    sufCan[x + 1] = true;
    for(int i = x; i >= 1; i--) {
        if(!sufCan[i + 1]) break;
        if(mxPos[i] < sufMin[i + 1]) sufCan[i] = true;
    }
    LL ans = 0;
    for(int i = 1; i <= x; i++) {
        int low = i, high = x, p = i - 1;
        while(low <= high) {
            int mid = low + high >> 1;
            if(!check(i, mid)) p = mid, low = mid + 1;
            else high = mid - 1;
        }
        ans += x - p;
    }
    printf("%lld\n", ans);
    return 0;
}

/*
*/