Luogu4137：Rmq Problem/mex

题面

Sol

# include <bits/stdc++.h>
# define IL inline
# define RG register
# define Fill(a, b) memset(a, b, sizeof(a))
using namespace std;
typedef long long ll;
const int _(2e5 + 5);

IL ll Input(){
RG char c = getchar(); RG ll x = 0, z = 1;
for(; c < '0' || c > '9'; c = getchar()) z = c == '-' ? -1 : 1;
for(; c >= '0' && c <= '9'; c = getchar()) x = (x << 1) + (x << 3) + (c ^ 48);
return x * z;
}

int n, q, bl[_], val[_], ans[_], cnt[_], sum[_];
struct Qry{
int l, r, id;
IL bool operator <(RG Qry B) const{
return bl[l] != bl[B.l] ? bl[l] < bl[B.l] : r < B.r;
}
} qry[_];

IL void Modify(RG int x, RG int d){
if(d > 0){
if(!cnt[x]) ++sum[x / 500];
++cnt[x];
}
else{
--cnt[x];
if(!cnt[x]) --sum[x / 500];
}
}

IL int Calc(){
RG int ret = 0;
for(RG int i = 0; ; ++i)
for(RG int j = 0; j < 500 && sum[i] != 500; ++j)
if(!cnt[i * 500 + j]) return i * 500 + j;
}

int main(RG int argc, RG char* argv[]){
n = Input(); q = Input();
RG int blo = sqrt(n);
for(RG int i = 1; i <= n; ++i){
val[i] = Input();
bl[i] = (i - 1) / blo + 1;
}
for(RG int i = 1; i <= q; ++i) qry[i] = (Qry){Input(), Input(), i};
sort(qry + 1, qry + q + 1);
for(RG int L = qry[1].l, R = qry[1].l - 1, i = 1; i <= q; ++i){
while(L < qry[i].l) Modify(val[L], -1), ++L;
while(L > qry[i].l) --L, Modify(val[L], 1);
while(R < qry[i].r) ++R, Modify(val[R], 1);
while(R > qry[i].r) Modify(val[R], -1), --R;
ans[qry[i].id] = Calc();
}
for(RG int i = 1; i <= q; ++i) printf("%d\n", ans[i]);
return 0;
}