cf 762C. Two strings

 1 #include<bits/stdc++.h> 
 2 #define LL long long 
 3 #define N 100005
 4 #define lowbit(x) x&(-x)
 5 using namespace std;
 6 inline int ra()
 7 {
 8     int x=0,f=1; char ch=getchar();
 9     while (ch<‘0‘ || ch>‘9‘) {if (ch==‘-‘) f=-1; ch=getchar();}
10     while (ch>=‘0‘ && ch<=‘9‘) {x=x*10+ch-‘0‘; ch=getchar();}
11     return x*f;
12 }
13 char a[N], b[N];
14 int fl[N], fr[N];
15 int la, lb, i, j, mid, l, r, a1, a2;
16 int main()
17 {
18     scanf("%s%s",a+1,b+1);
19     la=strlen(a+1); lb=strlen(b+1);
20     for (i=1,fl[0]=j=0; b[i]; i++)
21     {
22         for (j++; j<=la && a[j]!=b[i]; j++);
23         fl[i]=j; 
24     }
25     for (i=lb, fr[lb+1]=j=la+1; b[i]; i--)
26     {
27         for (j--; j>0 && a[j]!=b[i]; j--);
28         fr[i]=j;
29     }
30     for (l=0,r=lb; l<=r;)
31     {
32         mid=(l+r)>>1;
33         for (i=0; i+mid<=lb; i++)
34             if (fl[i]<fr[i+mid+1]) break;
35         if (i+mid<=lb) a1=i,a2=mid+i+1,r=mid-1;
36         else l=mid+1;
37     }
38     for (int i=1; i<=a1; i++) putchar(b[i]);
39     for (int i=a2; i<=lb; i++) putchar(b[i]);
40     if (a2-a1>lb) putchar(‘-‘);
41     return 0;
42 }