Write an efficient function to return maximum occurring character in the input string e.g., if input string is “test” then function should return ‘t’.
One obvious approach to solve this problem would be to sort the input string and then traverse through the sorted string to find the character which is occurring maximum number of times. Let us see if we can improve on this. So we will use a technique called ‘Hashing’. In this, when we traverse through the string, we would hash each character into an array of ASCII characters.
Input string = “test” 1: Construct character count array from the input string. count['e'] = 1 count['s'] = 1 count['t'] = 2 2: Return the index of maximum value in count array (returns ‘t’).
Typically, ASCII characters are 256, so we use our Hash array size as 256. But if we know that our input string will have characters with value from 0 to 127 only, we can limit Hash array size as 128. Similarly, based on extra info known about input string, the Hash array size can be limited to 26.
Max occurring character is s
Time Complexity: O(n)
Space Complexity: O(1) — Because we are using fixed space (Hash array) irrespective of input string size.
If more than one characters have the same count and that count is maximum then the function returns the first character with maximum count in input string. For example if input string is “test sample” then there are three characters with same and maximum count two i.e. “t”, “e” and “s” but our program will result “t” because “t” comes first in input string. Similarly, the output for “cbbbbccc” would be “c”.
As an variation to the above program, think about the change in code if you want to output “e” for input “test sample” i.e. the character of maximum count and that character should be of least ASCII value. For “cbbbbccc”, output should be “b”. Try it out !
Also, can you think of improvement if we can avoid two loopings in the above? Basically, you need to figure out if we can solve the same problem with one loop itself instead of two loops.
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