[RMQ] [线段树] POJ 3368 Frequent Values

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<cmath>
#include<vector>
#include<queue>
#include<stack>
#include<map>
#include<set>
#include<string>
#include<iomanip>
#include<ctime>
#include<climits>
#include<cctype>
#include<algorithm>
#ifdef WIN32
#define AUTO "%I64d"
#else
#define AUTO "%lld"
#endif
using namespace std;
const int INF=0x3f3f3f3f;
const int maxn=100005;
const int maxd=20;
int n,q;
int a[maxn];
int sum[maxn];
int to[maxn];
inline bool init()
{
    if(!~scanf("%d%d",&n,&q) || !n) return false;
    for(int i=1;i<=n;i++) scanf("%d",a+i);
    sum[1]=1;
    for(int i=2;i<=n;i++)
        if(a[i-1]^a[i]) sum[i]=1;
        else sum[i]=sum[i-1]+1;
    to[n]=n;
    for(int i=n-1;i;i--)
        to[i] = a[i]^a[i+1]? i : to[i+1];
    return true;
}
int dp[maxn][maxd];
void ST()
{
    for(int i=1;i<=n;i++) dp[i][0] = sum[i];
    int k=0;
    while( (1<<k+1) <= n ) k++;
    for(int j=1;j<=k;j++)
        for(int i=1;i+(1<<j)-1<=n;i++)
            dp[i][j] = max( dp[i][j-1] , dp[i+(1<<j-1)][j-1] ); // j-1 moved !!!
}
inline int RMQ(int x,int y)
{
    if (x>y) return -INF; // INF here to make the case extinct!!
    int k=0;
    while( (1<<k+1) <= (y-x+1) ) k++;
    return max(dp[x][k] , dp[y-(1<<k)+1][k]);
}
int main()
{
    freopen("fre.in","r",stdin);
    freopen("fre.out","w",stdout);
    while(init())
    {
        ST();
        for(int i=1;i<=q;i++)
        {
            int x,y;
            scanf("%d%d",&x,&y);
            printf("%d\n",max(sum[min(to[x],y)]-sum[x]+1 , RMQ(to[x]+1,y)));
        }
    }
    return 0;
}