2019杭電多校第一場string(序列自動機)

#include<iostream>
#include<cstring>
#include<cstdio>
#include<queue>
#include<cstdlib>
#include<cmath>
#include<stack>
#include<map>
#include<string>
#include<vector>
#include<set>
#include<bitset>
#include<algorithm>
using namespace std;
#define ll long long
#define INF 0x3f3f3f3f
#define LINF 0x3f3f3f3f3f3f3f3f
#define ull unsigned long long
#define endl '\n'
#define clr(a, b) memset(a, b, sizeof(a))
#define lowbit(x) x & -x
#define lson rt << 1, l, mid
#define rson rt << 1 | 1, mid + 1, r
#define next nxt
#define PB push_back
#define POP pop_back
const double pi = acos(-1);
const int maxn = 1e5 + 10;
const int maxm = (maxn<<5) + 5;
const ll mod = 998244353;
const int hash_mod = 19260817;
int k, len;
char s[maxn], ans[maxn];
int next[maxn][30], suf[maxn][30], now[30], num[30],use[30], l[30], r[30];
void init(){
    clr(now, -1);
    clr(num, 0);
    for(int i = len ; i >= 0 ; -- i){
        for(int j = 0 ; j < 26 ; ++ j){
            next[i][j] = now[j];
            suf[i][j] = num[j];;
        }
        num[s[i]-'a'] ++;
        now[s[i]-'a'] = i;
    }
}
int check(int x, int c, int cnt){
    if(use[c] + 1 > r[c]) return 0;
    int need = 0;
    use[c] ++;
    int id = next[cnt][c];
    if(id == -1) return 0;
    for(int i = 0 ; i < 26 ; ++ i) need += max(0, l[i] - use[i]);
    if(need > k - x){
        use[c] --;
        return 0;
    }
    for(int i = 0 ; i < 26 ; ++ i){
        if(use[i] + suf[id][i] < l[i]){
            use[c] --;
            return 0;
        }
    }
    return 1;
}
int main()
{
    //freopen("E://1005.in","r",stdin); //輸入重定向，輸入數據將從in.txt文件中讀取
    //freopen("E://outt.txt","w",stdout); //輸出重定向，輸出數據將保存在out.txt文件中
    while(~scanf("%s %d", s+1, &k)){
        for(int i = 0 ; i < 26 ; ++ i){
            scanf("%d %d", &l[i], &r[i]);
        }
        clr(suf, 0); clr(next, 0); clr(use, 0);
        len = strlen(s + 1);
        init();
        int cnt = 0, flag  = 0;
        for(int i = 1 ; i <= k ; ++ i){
            flag = 0;
            for(int j = 0 ; j < 26 ; ++ j){
                if(check(i, j, cnt)){
                    cnt = next[cnt][j];
                    ans[i] = j + 'a';
                    flag = 1;
                    break;
                }
            }
            if(!flag){
                flag = -1;
                break;
            }
        }
        if(flag == -1){
            cout << "-1" << endl;
        }
        else{
            for(int i = 1 ; i <= k ; ++ i) cout << ans[i];
            cout << endl;
        }
    }
    return 0;
}