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2020-05-25-FirstUniqueCharacterInAString

Leetcode-64

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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.

solution

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/**
* @param {string} s
* @return {number}
*/
var firstUniqChar = function(s) {
for(var i=0;i<s.length;i++){
var flag = false;
for(var j=0;j<s.length;j++){
if(i==j)continue;
if(s[i]==s[j])flag=true;
}
if(!flag)return i;

}
return -1;
};
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class Solution {
public int firstUniqChar(String s) {
HashMap<Character, Integer> count = new 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;
}
}