11235 - Frequent values

《算法竞赛入门经典-训练指南》P198

记录一下区间的左右边界就可以了

#include <iostream>

#include <stack>

#include <queue>

#include <cstdio>

#include <cstdlib>

#include <cmath>

#include <set>

#include <vector>

#include <cstring>

#include <algorithm>



#define INF 0x7fffffff

#define N 100010

#define M 1000010

#define LL long long

#define mod 95041567



using namespace std;



int arr[N];

int num[N][3];

int dp[N][20];



void RMQ_init(int len){

    for(int j = 1; (1 << j) <= len; ++ j)

        for(int i = 1; i + (1 << j) - 1 < len; ++ i)

            dp[i][j] = max(dp[i][j - 1], dp[i + (1 << (j - 1))][j - 1]);

}



int RMQ(int L, int R){

    if(R < L) return 0;

    else if(R == L) return dp[R][0];

    int k = 0;

    while((1 << (k + 1)) <= R - L + 1) ++ k;

    return max(dp[L][k], dp[R - (1 << k) + 1][k]);

}



int main()

{

    int n, q;

   // freopen("in.txt","r",stdin);

    while(scanf("%d", &n) != EOF){

        if(! n) break;

        scanf("%d", &q);

        for(int i = 0; i < n; ++ i) scanf("%d", &arr[i]);

        for(int i = 0; i <= n + 2; ++ i)

            for(int j = 0; j <= 20; ++ j)

                dp[i][j] = 0;

        arr[n] = INF;

        int p = 0;

        int len = 0;

        for(int i = 1; i <= n; ++ i)

            if(arr[i] != arr[i - 1]){

                for(int j = p; j <= i - 1; ++ j){

                    num[j][0] = i - 1;

                    num[j][1] = p;

                    num[j][2] = len;

                }

                dp[len ++][0] = i - p;

                p = i;

            }

        RMQ_init(len);

        int L, R;

        for(int i = 0; i < q; ++ i){

            scanf("%d %d", &L, &R);

            if(arr[L - 1] == arr[R - 1]){

                printf("%d\n", R - L + 1);

                continue;

            }

            //printf("%s\n", "++");

            p = num[L - 1][0] - (L - 1) + 1;

            p = max(p, R - num[R - 1][1]);

            p = max(p, RMQ(num[L - 1][2] + 1, num[R - 1][2] - 1));

            printf("%d\n", p);

        }

    }

    return 0;

}