题意

题目链接

Sol

感觉自己已经老的爬不动了。。

想了一会儿，大概用个不删除莫队+带撤销并查集就能搞了吧，\(n \sqrt{n} logn\)应该卡的过去

不过不删除莫队咋写来着？。。。。跑去学。。

带撤销并查集咋写来着？。。。。跑去学。。。

发现自己的带撤销并查集是错的，，自己yy着调了1h终于过了大数据。。

#include<bits/stdc++.h>

#define Pair pair<int, int>

#define MP(x, y) make_pair(x, y)

#define fi first

#define se second

//#define int long long

#define LL long long

#define Fin(x) {freopen(#x".in","r",stdin);}

#define Fout(x) {freopen(#x".out","w",stdout);}

#define pb(x) push_back(x)

using namespace std;

const int mod = 1e9 + 7;

const int MAXN = 1e6 + 10;

template <typename A, typename B> inline bool chmin(A &a, B b){if(a > b) {a = b; return 1;} return 0;}

template <typename A, typename B> inline bool chmax(A &a, B b){if(a < b) {a = b; return 1;} return 0;}

template <typename A, typename B> inline LL add(A x, B y) {if(x + y < 0) return x + y + mod; return x + y >= mod ? x + y - mod : x + y;}

template <typename A, typename B> inline void add2(A &x, B y) {if(x + y < 0) x = x + y + mod; else x = (x + y >= mod ? x + y - mod : x + y);}

template <typename A, typename B> inline LL mul(A x, B y) {return 1ll * x * y % mod;}

template <typename A, typename B> inline void mul2(A &x, B y) {x = (1ll * x * y % mod + mod) % mod;}

template <typename A> inline void debug(A a){cout << a << '\n';}

template <typename A> inline LL sqr(A x){return 1ll * x * x;}

inline int read() {

    char c = getchar(); int x = 0, f = 1;

    while(c < '0' || c > '9') {if(c == '-') f = -1; c = getchar();}

    while(c >= '0' && c <= '9') x = x * 10 + c - '0', c = getchar();

    return x * f;

}

int N, M, a[MAXN], belong[MAXN], block, ans[MAXN], cnt, fa[MAXN];

struct Q {

    int l, r, id;

    bool operator < (const Q &rhs) const{

        return r < rhs.r;

    }

};

vector<Q> q[MAXN];

int SolveBlock(int x, int y) {

    if(x == y) return 1;

    vector<int> v;

    for(int i = x; i <= y; i++) v.pb(a[i]);

    sort(v.begin(), v.end());

    int res = 1, now = 1;

    for(int i = 1; i < v.size(); i++)

		now = (v[i] == v[i - 1] + 1 ? now + 1 : 1), chmax(res, now);

    return res;

}

int inder[MAXN], Top, ha[MAXN], cur, mx;

struct Node {

    int x, deg;

}S[MAXN];

int find(int x) {

	return fa[x] == x ? x : find(fa[x]);

}

void unionn(int x, int y) {

    x = find(x); y = find(y);

    if(x == y) return;

    if(inder[x] < inder[y]) swap(x, y);

	chmax(mx, inder[x] + inder[y]);

    fa[y] = x;

    S[++Top] = (Node) {y, inder[y]};

    S[++Top] = (Node) {x, inder[x]};//tag

    inder[x] += inder[y];

}

void Delet(int cur) {

    while(Top > cur) {

        Node pre = S[Top--];

        fa[pre.x] = pre.x;

        inder[pre.x] = pre.deg;

    }

}

void Add(int x) {

    ha[x] = 1;

    if(ha[x - 1]) unionn(x - 1, x);

    if(ha[x + 1]) unionn(x, x + 1);

}

void solve(int i, vector<Q> &v) {

	memset(ha, 0, sizeof(ha));

	Top = 0; int R = min(N, i * block) + 1;

    int ql = R, qr = ql - 1;//tag

    cur = 0, mx = 1;

    for(int i = 1; i <= N; i++) fa[i] = i, inder[i] = 1;

    for(int i = 0; i < v.size(); i++) {

    	Q x = v[i];

        while(qr < x.r) Add(a[++qr]);

        cur = mx; int pre = Top;

        while(ql > x.l) Add(a[--ql]);

        ans[x.id] = mx;

        mx = cur;

        Delet(pre);

        while(ql < R) ha[a[ql++]] = 0;

    }

}

signed main() {

    int mx = 0;

    N = read(); M = read(); block = sqrt(N);

    for(int i = 1; i <= N; i++) a[i] = read(), belong[i] = (i - 1) / block + 1, chmax(mx, belong[i]);

    for(int i = 1; i <= M; i++) {

        int x = read(), y = read();

        if(belong[x] == belong[y]) ans[i] = SolveBlock(x, y);

        else q[belong[x]].push_back({x, y, i});

    }

    for(int i = 1; i <= mx; i++) sort(q[i].begin(), q[i].end()), solve(i, q[i]);

    for(int i = 1; i <= M; i++) printf("%d\n", ans[i]);

    return 0;

}

/*

8 3

3 1 7 2 4 5 8 6

1 6

1 3

2 4

*/