387. First Unique Character in a String

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.

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解题思路：用map存储字符的个数，遍历两遍，确认第一个字符。

public class Solution {
public int firstUniqChar(String s) {
Map<Character, Integer> map2 = new HashMap<Character,Integer>();
int len = s.length();
for(int i = 0; i < len; i++)
{
if(map2.containsKey(s.charAt(i)))
{
int value = map2.get(s.charAt(i));
value ++;
map2.put(s.charAt(i),value);
}else{
map2.put(s.charAt(i),1);
}
}

for(int i = 0; i < len; i++)
{
if(map2.get(s.charAt(i))== 1)
{
return i;
}
}
return -1;

}
}