UVA - 11235 —— Frequent values 【RMQ】

#include <iostream>
#include <cstdio>
#include <cstring>
#include <string>
#define INF 0x3f3f3f3f
using namespace std;
const int MAXN = 100000 + 5, MAXK = 17 + 5;
int d[MAXN][MAXK];
int val[MAXN], num[MAXN];
int id[MAXN], L[MAXN], R[MAXN];
int size;

void build(int n)
{
    for(int i=1; i<=n; i++) {
        d[i][0] = num[i];
    }
    
    for(int j=1; (1<<j) <= n; j++) {
        for(int i=1; i + (1 << j) - 1 <= n; i++) {
            d[i][j] = max(d[i][j-1], d[i+(1<<(j-1))][j-1]);
        }
    }
}

int query(int l, int r)
{
    if(l>r)    return -INF; // 是必要的，因为仔细考虑一下，是有可能出现该异常的！
    int w = r - l + 1;
    int x = 0;
    while((1<<x+1) <= w) x++;
    return    max(d[l][x], d[r-(1<<x)+1][x]);
}

int main ()
{
    int n, q, l, r;
    while(scanf("%d", &n) != EOF && n) {
        scanf("%d", &q);
        size = 1;
        int pre, x;
        for(int i=1; i<=n; i++) {
            scanf("%d", &x);
            if(i==1) {
                val[size] = x;
                num[size] = 1;
                id[i] = size;
                L[size] = i;
            } else if(x != pre) {
                R[size] = i-1;
                size++;
                
                val[size] = x;
                num[size] = 1;
                id[i] = size;
                L[size] = i;
            } else {
                num[size]++;
                id[i] = size;
            }
            pre = x;
        }
        R[size] = n;
        
        build(size);
        
        while(q--) {
            scanf("%d%d", &l, &r);
            int maxn;
            if(id[l] == id[r]) {
                maxn = r - l + 1;
            } else {
                maxn = R[id[l]] - l + 1;
                maxn = max(maxn, r - L[id[r]] + 1);
                maxn = max(maxn, query(id[l]+1, id[r]-1));
            }
        
            printf("%d\n", maxn);
        }
    }
    return 0;
}