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

You're given a string. Identify every character that shows up more than once, and report each one together with how many times it occurs.

Treat uppercase and lowercase as distinct characters — 'a' and 'A' don't count as the same.

Input Format
Implement findDuplicates(str). Inputs below show JavaScript function arguments; there is no stdin parsing.
Output Format
Return the result described in the statement.

Sample Input and Output

Example 1 · Run Sample

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

Example 2

Input
str = ""
Output
{}
Constraints
  • 0 <= str.length <= 10^5
  • str consists of printable ASCII characters.
Test Cases (2)
Case 1
Args: ["programming"] Expected: {"r":2,"g":2,"m":2}
Case 2
Args: [""] Expected: {}
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.

javascript
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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JavaScript