387. First Unique Character in a String(easy)

Easy

118886FavoriteShare

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.

 

哈希表法使用map：

C++：

/*
 * @Autor: SourDumplings
 * @Date: 2019-09-19 09:04:58
 * @Link: https://github.com/SourDumplings/
 * @Email: changzheng300@foxmail.com
 * @Description: https://leetcode.com/problems/first-unique-character-in-a-string/
 */

class Solution
{
public:
    int firstUniqChar(string s)
    {
        map<char, int> m;
        for (auto &&c : s)
        {
            if (m.find(c) == m.end())
            {
                m[c] = 1;
            }
            else
            {
                ++m[c];
            }
        }
        int l = s.length();
        for (int i = 0; i < l; i++)
        {
            char c = s[i];
            if (m[c] == 1)
            {
                return i;
            }
        }
        return -1;
    }
};

哈希表法自己写哈希表：

Java：

import java.util.Arrays;

/*
 * @Autor: SourDumplings
 * @Date: 2019-09-19 09:09:24
 * @Link: https://github.com/SourDumplings/
 * @Email: changzheng300@foxmail.com
 * @Description: https://leetcode.com/problems/first-unique-character-in-a-string/
 */

class Solution
{
    public int firstUniqChar(String s)
    {
        int[] hashTable = new int[26];
        Arrays.fill(hashTable, 0);
        int l = s.length();
        for (int i = 0; i < l; i++)
        {
            char c = s.charAt(i);
            ++hashTable[c - 'a'];
        }
        for (int i = 0; i < l; i++)
        {
            char c = s.charAt(i);
            if (hashTable[c - 'a'] == 1)
            {
                return i;
            }
        }
        return -1;
    }
}