The Preliminary Contest for ICPC China Nanchang National Invitational M题 Subsequence

枚举给个字符最早出现的位置就可以了
#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e6 + 5;
char s[maxn];
int pos[maxn][30];
int dis[maxn];
int main() {
  scanf("%s", s + 1);
  int n = strlen(s + 1);
  for(int i = n; i >= 1; i--) {
    for(int j = 0; j <= 26; j++) {
      pos[i][j] = pos[i + 1][j];
    }
    pos[i][s[i] - 'a'] = i;
    dis[s[i] - 'a'] = i;
  }
  scanf("%d", &n);
  for(int i = 1; i <= n; i++) {
    scanf("%s", s + 1);
    int m = strlen(s + 1); 
    int start = dis[s[1] - 'a'];
    if(start == 0) {
      printf("NO\n");
      continue;
    }
    int flag = 1;
    for(int j = 2; j <= m; j++) {
      if(pos[start + 1][s[j] - 'a'] == 0) {
        flag = 0;
        break;
      }
      start = pos[start + 1][s[j] - 'a'];
    }
    if(flag) {
      printf("YES\n");
    } else {
      printf("NO\n");
    }
  } 
  return 0;
}