Codechef SEPT17 CookOff - Subsequence Equality Problem Code: LIKECS01

Problem : https://www.codechef.com/problems/LIKECS01

Chef Tobby is playing a rapid fire with Bhuvan. He gives Bhuvan a string S and each time, Bhuvan has to guess whether there exists 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 contain 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.

Input constraints

1 ≤ T ≤ 1000 1 ≤ length of S ≤ 100

Sample Input

4 likecs venivedivici bhuvan codechef

Sample Output

no yes no yes

Explanation

In test case 2, one of the possible equal subsequence is "vi" and "vi". (one at position 3 and other at 7, assuming 0-based indexing).
In test case 4, one of the possible equal subsequence is "ce" and "ce". (one at position 3 and other at 6, assuming 0-based indexing).

Solution

    #include <iostream>
    #include <set>
    using namespace std;
    int main()
    {
        int t;
        cin >> t;
        while (t--) {
            set<char> st;
            string s;
            cin >> s;
            for (int i = 0; i < s.length(); i++)
                st.insert(s[i]);
            if (st.size() == s.length())
                cout << "no" << endl;
            else
                cout << "yes" << endl;
        }

        return 0;
    }