387. First Unique Character in a String.md

387. First Unique Character in a String

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leetcode-cn Daily Challenge on December 23th, 2020.

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Difficulty : Easy

Related Topics : HashTable、String

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

Examples:

s = "leetcode"
return 0.

s = "loveleetcode"
return 2.

Note

• You may assume the string contains only lowercase English letters.

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Solution

• mine
  • Java
    • Runtime: 4 ms, faster than 98.88%, Memory Usage: 39.2 MB, less than 90.15% of Java online submissions

      //O(N)time
      //O(1)space
      public int firstUniqChar(String s) {
          char[] arr = s.toCharArray();
          int[] record = new int[26];
          for(char c : arr){
              record[c - 'a']++;
          }
          for(int i = 0; i < arr.length; i++){
              if(record[arr[i] - 'a'] == 1) return i;
          }
          return -1;
      }
      

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