387. First Unique Character in a String

📝 Problem Details

• Title: 387. First Unique Character in a String
• Link: https://leetcode.com/problems/first-unique-character-in-a-string/
• Difficulty: Easy
• Tags/Categories: Hashmap Strings

💡 Explanation of Solution

Two Pass Through Approach:

1. iterate through the string, building a frequency map for the frequency of each character 
2. iterate through the string, checking if the current character's frequency in the map is == 1, if it is , return i

- otherwise return -1

⌛ Complexity Analysis

Time Complexity: O(n)
Space Complexity: O(n)

💻 Implementation of Solution

class Solution {
public:
    int firstUniqChar(string s) {
        unordered_map<char, int> freqMap;
        for(int i=0; i < s.size(); i++) {
            freqMap[s[i]]++;
        }
        for(int i=0; i < s.size(); i++) {
            if(freqMap[s[i]] == 1) return i;
        }
        return -1;
    }
};