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387.First-Unique-Character-in-a-String

387. First Unique Character in a String
题目地址
​https://leetcode.com/problems/first-unique-character-in-a-string/​
题目描述
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.
代码
Approach #1  Linear time solution
Complexity Analysis
Time complexity : O(N) since we go through the string of length N two times.
Space complexity : O(N) since we have to keep a hash map with N elements.
class Solution {
  public int firstUniqChar(String s) {
        HashMap<Character, Integer> count = new HashMap<Character, Integer>();
    int n = s.length();
    for (int i = 0; i < n; i++) {
      char c = s.charAt(i);
      count.put(c, count.getOrDefault(c, 0) + 1);
    }
​
    for (int i = 0; i < n; i++) {
      if (count.get(s.charAt(i)) == 1) {
        return i;
      }
    }
​
    return -1;
  }
}
#2
public class Solution {
    public int firstUniqChar(String s) {
        int count [] = new int[26];
        for (int i = 0; i < s.length(); i ++) {
          count[s.charAt(i) - 'a'] ++;
        }
​
        for (int i = 0; i < s.length(); i ++) {
           if (count[s.charAt(i) - 'a'] == 1) {
              return i;
            }
        } 
        return -1;
    }
}

383.Ransom-Note

4.Median-of-Two-Sorted-Arrays

Last modified 3yr ago