Print all the duplicate characters in a string Easy 0 attempts
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Print all the duplicate characters in a string

Easy StringHash Table GeeksforGeeks

Given a string, find all characters that appear more than once and print each duplicate character along with its count.

The comparison is case-sensitive — 'a' and 'A' are treated as different characters.

Examples

Input: "programming"
Output: { r: 2, g: 2, m: 2 }

Input: "hello world"
Output: { l: 3, o: 2 }

Input: "abcde"
Output: {} (no duplicates)

Constraints

  • The string can contain letters, digits, spaces, and special characters.
  • An empty string should return no duplicates.
Sample Input
s = "test string"
Sample Output
t: 3, s: 2
Constraints
  • 1 <= s.length <= 10^5
  • s consists of printable ASCII characters
Topics
StringHash Table

Count each character's frequency using a hash map in a single pass. Then filter for characters with a count greater than one.

function findDuplicates(str) {
  const freq = {};
  for (const ch of str) {
    freq[ch] = (freq[ch] || 0) + 1;
  }

  const duplicates = {};
  for (const [ch, count] of Object.entries(freq)) {
    if (count > 1) {
      duplicates[ch] = count;
    }
  }
  return duplicates;
}

Time: O(n) — single pass to count, single pass to filter. Space: O(k) where k is the number of distinct characters.

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