HDU5558 Alice's Classified Message(合肥区域赛 后缀数组)

当初合肥区域赛的题(现场赛改了数据范围就暴力过了)，可惜当初后缀数组算法的名字都没听过，现在重做下。

i从1到n - 1，每次枚举rank[i]附近的排名，并记录当起点小于i时的LCP(rank[i], d)的最大值，或是在LCP不变时更新起点。

 

#include<cstdio>
#include<iostream>
#include<algorithm>
#include<cstring>
#include<cstdlib>
using namespace std;
const int N = 110008, INF = 0x3F3F3F3F;

int val[N], ws0[N], wa[N], wb[N];
int sa[N], rk[N], height[N];

char str[N];

bool cmp(int str[], int a, int b, int l){
    return str[a] == str[b] && str[a + l] == str[b + l];
}

void da(char str[], int n, int m){
    int *x = wa, *y = wb;

    memset(ws0, 0, sizeof(ws0));
    for(int i = 0; i < n; i++)
        ws0[x[i] = str[i]]++;

    for(int i = 1; i < m; i++)
        ws0[i] += ws0[i - 1];

    for(int i = n - 1; i >= 0; i--)
        sa[--ws0[ x[i]] ] = i;

    for(int j = 1, p = 1; p < n; j *= 2, m = p){
        p = 0;
        for(int i = n - j; i < n; i++)
            y[p++] = i;
        for(int i = 0; i < n; i++)
            if(sa[i] >= j)
                y[p++] = sa[i] - j;
        for(int i = 0; i < n; i++)
            val[i] = x[ y[i] ];

        memset(ws0, 0, sizeof(ws0));
        for(int i = 0; i < n; i++)
            ws0[val[i]]++;

        for(int i = 1; i < m; i++)
            ws0[i] += ws0[i - 1];

        for(int i = n - 1; i >= 0; i--)
            sa[--ws0[ val[i] ]] = y[i];

        swap(x, y);
        x[sa[0]] = 0;
        p = 1;
        for(int i = 1; i < n; i++)x[sa[i]] = cmp(y, sa[i - 1], sa[i], j)? p - 1:p++;
    }
}

void calHeight(char str[], int n){
    for(int i = 1; i <= n; i++){
        rk[ sa[i] ] = i;
    }
    int k = 0;
    for(int i = 0; i < n; i++){
        if(k){
            k--;
        }
        int j = sa[rk[i] - 1];
        while(str[i + k] == str[j + k]){
            k++;
        }
        height[rk[i]] = k;
    }
}

int rmq[N][20], tab[N];

void initaskRMQ(int n){
    tab[1] = 0;
    for(int i = 2; i <= n; i++){
        tab[i] = ( (i & (i - 1)) == 0)? tab[i - 1] + 1:tab[i - 1];
    }
    for(int i = 1; i <= n; i++){
        rmq[i][0] = height[i];
    }
    for(int i = 1; i <= tab[n]; i++){
        for(int j = 1; j <= n + 1 - (1 << i); j++){
            int a = rmq[j][i - 1];
            int b = rmq[j + (1 <<(i - 1))][i - 1];
            rmq[j][i] = min(a, b);
        }
    }
}

int askRMQ(int a, int b){
    int k = tab[b -a + 1];
    b -= (1 << k ) - 1;
    return min(rmq[a][k], rmq[b][k]);
}

int LCP(int a, int b){
    if(a > b){
        swap(a, b);
    }
    return askRMQ(a + 1, b);
}


int main(){
    int t;
    cin>>t;
    for(int cas = 1; cas <= t; cas++){
        scanf("%s", str);
        int n = strlen(str);
        da(str, n + 1, 'z' + 1);
        calHeight(str, n);

        initaskRMQ(n);
        printf("Case #%d:\n", cas);
        printf("%d %d\n", -1, str[0]);
        for(int i = 1; i < n; ){
            int st = INF, k = 1;
            int d = rk[i] + 1;
            int tp;
            while(d <= n && (tp = LCP(d, rk[i])) >= k){
                if(sa[d] < i){
                    if(tp > k){
                        k = tp;
                        st = sa[d];
                    }else{
                        if(sa[d] < st){
                            st = sa[d];
                        }
                    }
                }
                d++;
            }

            d = rk[i] - 1;
            while(d >= 1 && (tp = LCP(d, rk[i])) >= k){
                if(sa[d] < i){
                    if(tp > k){
                        k = tp;
                        st = sa[d];
                    }else{
                        if(sa[d] < st){
                            st = sa[d];
                        }
                    }
                }
                d--;
            }
            if(st < i){
                printf("%d %d\n", k, st);
                i += k;
            }else{
                printf("%d %d\n", -1, (int)str[i]);
                i++;
            }
        }
    }
    return 0;
}

　　加油吧! fighting!!!