387. First Unique Character in a String

Given a string, find the first non-repeating character in it and return it's index. If it doesn't exist, return -1.

Examples:

s = "leetcode"
return 0.

s = "loveleetcode",
return 2.

Note: You may assume the string contain only lowercase letters.
---

First unique character means we have to check all characters, time complexity is linear

Time - O(n)

Space - O(1)

	class Solution {
	public int firstUniqChar(String s) {
	int[] freq = new int[26];

	for (int i = 0; i < s.length(); i++) {
	freq[s.charAt(i) - 'a']++;
	}

	for (int i = 0; i < s.length(); i++) {
	if (freq[s.charAt(i) - 'a'] == 1) {
	return i;
	}
	}
	return -1;
	}
	}

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