LeetCode_387. First Unique Character in a String

Posted 2020-11-23 邓戈麟

 

387. First Unique Character in a String

Easy

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.

 

package leetcode.easy;

public class FirstUniqueCharacterInAString {
	public int firstUniqChar(String s) {
		java.util.HashMap<Character, Integer> count = new java.util.HashMap<Character, Integer>();
		int n = s.length();
		// build hash map : character and how often it appears
		for (int i = 0; i < n; i++) {
			char c = s.charAt(i);
			count.put(c, count.getOrDefault(c, 0) + 1);
		}

		// find the index
		for (int i = 0; i < n; i++) {
			if (count.get(s.charAt(i)) == 1)
				return i;
		}
		return -1;
	}

	@org.junit.Test
	public void test() {
		System.out.println(firstUniqChar("leetcode"));
		System.out.println(firstUniqChar("loveleetcode"));
	}
}