387. First Unique Character in a String

Description

Given a string s, find the first non-repeating character in it and return its index. If it does not exist, return -1.

 

Example 1:

Input: s = "leetcode"
Output: 0

Example 2:

Input: s = "loveleetcode"
Output: 2

Example 3:

Input: s = "aabb"
Output: -1

 

Constraints:

  • 1 <= s.length <= 105
  • s consists of only lowercase English letters.

Solutions

Solution 1

Python Code
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class Solution:
    def firstUniqChar(self, s: str) -> int:
        cnt = Counter(s)
        for i, c in enumerate(s):
            if cnt[c] == 1:
                return i
        return -1

Java Code
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class Solution {
    public int firstUniqChar(String s) {
        int[] cnt = new int[26];
        int n = s.length();
        for (int i = 0; i < n; ++i) {
            ++cnt[s.charAt(i) - 'a'];
        }
        for (int i = 0; i < n; ++i) {
            if (cnt[s.charAt(i) - 'a'] == 1) {
                return i;
            }
        }
        return -1;
    }
}

C++ Code
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class Solution {
public:
    int firstUniqChar(string s) {
        int cnt[26]{};
        for (char& c : s) {
            ++cnt[c - 'a'];
        }
        int n = s.size();
        for (int i = 0; i < n; ++i) {
            if (cnt[s[i] - 'a'] == 1) {
                return i;
            }
        }
        return -1;
    }
};

Go Code
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func firstUniqChar(s string) int {
	cnt := [26]int{}
	for _, c := range s {
		cnt[c-'a']++
	}
	for i, c := range s {
		if cnt[c-'a'] == 1 {
			return i
		}
	}
	return -1
}

TypeScript Code
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function firstUniqChar(s: string): number {
    const cnt = new Array(26).fill(0);
    for (const c of s) {
        cnt[c.charCodeAt(0) - 97]++;
    }
    for (let i = 0; i < s.length; i++) {
        if (cnt[s.charCodeAt(i) - 97] === 1) {
            return i;
        }
    }
    return -1;
}

JavaScript Code
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/**
 * @param {string} s
 * @return {number}
 */
var firstUniqChar = function (s) {
    const cnt = new Array(26).fill(0);
    for (const c of s) {
        ++cnt[c.charCodeAt() - 'a'.charCodeAt()];
    }
    for (let i = 0; i < s.length; ++i) {
        if (cnt[s[i].charCodeAt() - 'a'.charCodeAt()] === 1) {
            return i;
        }
    }
    return -1;
};

PHP Code
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class Solution {
    /**
     * @param String $s
     * @return Integer
     */
    function firstUniqChar($s) {
        for ($i = 0; $i < strlen($s); $i++) {
            $hashtable[$s[$i]]++;
        }
        for ($i = 0; $i < strlen($s); $i++) {
            if ($hashtable[$s[$i]] == 1) {
                return $i;
            }
        }
        return -1;
    }
}