Luogu P3709 大爷的字符串题

题目传送门

阅读理解题

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真正题意

求区间众数的出现次数，输出时在前面加个负号

题解

莫队！

用tong[i]表示数i出现的次数cnt[i]表示出现i次的数有多少个

• 加入一个数时，ans = max(tong[i], ans)
• 删除一个数时，要注意如果tong[i] == ans && !cnt[tong[i]]，需要--ans

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#define MAXN 200010
#define LL long long
using namespace std;
LL read() {
    LL k = 0, f = 1; char c = getchar();
    while(c < '0' || c > '9') {
        if(c == '-') f = -1;
        c = getchar();
    }
    while(c >= '0' && c <= '9')
      k = k * 10 + c - 48, c = getchar();
    return k * f;
}
int a[MAXN], b[MAXN], tot;
struct zzz {
    int l, r, pos;
}q[MAXN];
int blo, tong[MAXN], cnt[MAXN], anss[MAXN];
bool cmp(zzz x, zzz y) {
    if(x.l / blo != y.l / blo) return x.l / blo < y.l / blo;
    else return x.r < y.r;
}
int main() {
    int n = read(), m = read(); blo = sqrt((double)n);
    for(int i = 1; i <= n; ++i)
        a[i] = b[i] = read();
    sort(a+1, a+n+1); tot = unique(a+1, a+n+1) - a - 1;
    for(int i = 1; i <= n; ++i) b[i] = lower_bound(a+1, a+tot+1, b[i]) - a;
    for(int i = 1; i <= m; ++i)
        q[i].l = read(), q[i].r = read(), q[i].pos = i;
    sort(q+1, q+m+1, cmp);

    int l = 1, r = 0, ans = 0;
    for(int i = 1; i <= m; ++i) {
        while(l < q[i].l) {
            --cnt[tong[b[l]]];
            if(tong[b[l]] == ans && !cnt[tong[b[l]]]) --ans;
            cnt[--tong[b[l]]]++; ++l;
        }
        while(r > q[i].r) {
            --cnt[tong[b[r]]];
            if(tong[b[r]] == ans && !cnt[tong[b[r]]]) --ans;
            cnt[--tong[b[r]]]++; --r;
        }
        while(l > q[i].l) {
            --l;
            --cnt[tong[b[l]]]; cnt[++tong[b[l]]]++;
            ans = max(ans, tong[b[l]]);
        }
        while(r < q[i].r) {
            ++r;
            --cnt[tong[b[r]]]; cnt[++tong[b[r]]]++;
            ans = max(ans, tong[b[r]]);
        }
        anss[q[i].pos] = ans;
    }
    for(int i = 1; i <= m; ++i) cout << -anss[i] << endl;
    return 0;
}