What is Character Frequency?

Character Frequency is a string-processing technique used to count how many times each character appears in a given string. It is commonly implemented using a HashMap (or dictionary) where each character is stored as a key and its occurrence count as the value.

Example

• Input String: "banana"
• Read 'b' → { b: 1 }
• Read 'a' → { b: 1, a: 1 }
• Read 'n' → { b: 1, a: 1, n: 1 }
• Read 'a' → { b: 1, a: 2, n: 1 }
• Read 'n' → { b: 1, a: 2, n: 2 }
• Read 'a' → { b: 1, a: 3, n: 2 }

The algorithm scans the string one character at a time. If the character already exists in the map, its count is increased. Otherwise, it is added with a frequency of 1.

Algorithm Steps

1. Create an empty HashMap (or Dictionary).
2. Traverse the string character by character.
3. For each character:
   • If already present, increment its count.
   • Otherwise insert it with count = 1.
4. Display all characters with their frequencies.