387. First Unique Character in a String

Problem:

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.

思路：

Solution (C++):

int firstUniqChar(string s) {
    int n = s.length(), i, j;
    if (n == 0) return -1;
    if (n == 1) return 0;
    set<char> st;
    for (i = 0; i < n-1; ++i) {
        if (st.find(s[i]) != st.end()) continue;
        else st.insert(s[i]);
        for (j = i+1; j < n; ++j) {
            if (s[i] == s[j]) break;
        }
        if (j == n) return i;
    }
    if (st.find(s[n-1]) == st.end()) return n-1;
    return -1;
}

性能：

Runtime: 80 ms  Memory Usage: 10.9 MB

思路：

Solution (C++):

性能：

Runtime: ms  Memory Usage: MB