Given a string of lowercase alphabets, the task is to find indexes of a substring with given power. Assume power of a to be 1, b to be 2, c to be 3 and so on. Here the power of a substring means the sum of the powers of all the characters in that particular substring.
Input: str = “geeksforgeeks” power = 36
Output: Substring from index 3 to 5 has power 36
Explanation: k = 11, s = 19, f = 6 i.e. k + s + e = 36.
Input: str = “aditya” power = 2
Output: No substring with given power exists.
1. Calculate powers of all substrings using nested for loops.
2. If the power of any substring equals the given power then print the indexes of the substring.
3. If no such substring exists then print “No substring with given power exists”.
Time Complexity: O (n ^ 2).
Efficient Approach: Use map to store the powers.
1. For each element check if curr_power – power exists in the map or not.
2. If it exists in the map it means that we have a substring present with given power, else we insert curr_power into the map and proceed to the next character.
3. If all characters of the string are processed and we didn’t find any substring with given power, then substring doesn’t exist.
Substring from index 3 to 5 has power 36
Time Complexity: O (n)
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