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Help needed with a problem
By Romok007, history, 7 years ago, In English

Hello everyone. It would be great if someone gives a solution for this problem https://www.codechef.com/problems/CZ17R2Q2. Thank you.

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7 years ago, hide # |
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Maintain a stack of length n. For every i-th element, if it is positive, push it into the stack. If it is negative, let's call it x. Check if stack.top() == -x. If yes, pop stack.top() and increase the counter by 2.

Solution complexity — O(n).

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    7 years ago, hide # ^ |
     
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    I think for the input : 1 2 3 -1. Your solution will give 0 as the answer whereas the ans should be 2. Correct me if i am wrong.

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      7 years ago, hide # ^ |
       
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      How do you get answer 2 for 1 2 3 -1 ?

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        7 years ago, hide # ^ |
         
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        The question asks for the longest balanced subsequence. So if we take 1 -1 as the subsequence from 1 2 3 -1, we end up with a balanced subsequence of length 2.

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          7 years ago, hide # ^ |
           
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          I guess you have to pick consecutive positions because for sample testcase 1 -1 2 3 -2 answer is 2 (1 and -1). The answer could be 4 (1, -1, 2, -2) if it would be allowed to pick any positions. So for input 1 2 3 -1 answer is 0.

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7 years ago, hide # |
 
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Basically, you have to find the largest subarray whose sum is equal to zero. You can look at my submission here

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