JavaScriptEasyStrings10 min
Find the first non-repeated character
Return the first character appearing exactly once, or the empty string if none exists. All input is valid JSON satisfying the constraints; do not mutate the meaning of values through type coercion. Interviewers use this problem to assess count first, then scan in original order.
Input
A JSON string on stdin.
Output
Print one compact JSON value: a string.
Constraints
0 <= string length <= 10000; ASCII characters only.
Example
Input
"swiss"
Output
"w"
Example 2 input
"1123"
Output
"2"
Boundary case: No unique character means an empty string
Public test cases (2)
Input
"swiss"
Expected output
"w"
Input
"aabb"
Expected output
""
Hints (2)
- Use a Map for character counts
- No unique character means an empty string
Target complexity: time O(n) · space O(n)