Complexity Analysis

Time Complexity: O(n²), for each character, we are iterating the entire string to count its occurrence.

Space Complexity: O(n), we are using an array to store the frequency of each character.

Optimal Approach

Algorithm

Create an integer array freq to store character occurrences.
Use a for loop to iterate through the string and increment the frequency of each character.
After the loop, print only those characters whose frequency is 1.
Each index of the freq array corresponds to a character: freq[0] for 'a', freq[1] for 'b', ..., freq[25] for 'z'.

Code

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