First Non-Repeating Character using Map/Unordered Map

Medium STL Containers

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Problem Statement

Write a C++ program using `std::unordered_map` to find the first non-repeating character in a string.

Input Format

A single word string S.

Output Format

Print the first non-repeating character or '$' if none exists.

Constraints

1 <= Length <= 100

Sample Input

leetcode

Sample Output

Explanation

Hash maps record frequencies in one pass, allowing $O(1)$ lookups for uniqueness checks.

Starter Code

#include <iostream>
#include <unordered_map>
#include <string>

int main() {
    std::string s;
    if (std::cin >> s) {
        // Write your frequency counting and first non-repeating character logic here

    }
    return 0;
}

Limits

Time Limit: 1s
Memory Limit: 256MB

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