Subsequence Equality Problem

Question:-

Chef Tobby is playing a rapid fire with Bhuvan. He gives Bhuvan a string S and each time, Bhuvan has to guess whether there exist 2 equal subsequences in the string or not.

Bhuvan got a perfect score in the game with Chef Tobby. However, Chef Tobby has now asked Bhuvan to write a program that will do this automatically given a string S. Bhuvan is an intelligent man but he does not know how to write a code. Can you help him?

Find two different subsequences such that they are equal in their value, more formally, find two sequences of indices (a₁, a₂, ..., a_k-1, a_k) and (b₁, b₂, ..., b_k-1, b_k) such that:

1. 1≤ a_i, b_i ≤ |S|
2. a_i < a_i+1 for all valid i
3. b_i < b_i+1 for all valid i
4. S_ai = S_bi for all valid i
5. there exist at least one i such that a_i is not equal to b_i .

Input section

The first line contains T, the number of test cases.

Each of the next T lines contains one string S each.

Input will only consist of lowercase English characters

Output section

For each test case, output "yes" or "no" (without quotes) as the solution to the problem.

Solution:

1. #include <stdio.h> #include <string.h> int main() { int t,i,len,flag; char str[101]; scanf("%d",&t); int arr[26]; while(t--) { flag=0; for(i=0;i<26;i++) arr[i]=0; scanf("%s",str); len=strlen(str); for(i=0;i<len;i++) { arr[str[i]-'a']++; if(arr[str[i]-'a']==2) { flag=1; break; } } if(flag==1) printf("yes\n"); else printf("no\n"); } return 0; }