typescript

First Unique Character

2020-07-14
exercises
1 min read

function firstUniqueChar(str: string) {
    let mem: {[key: string]: number} = {}
    for (let ch of str) {
        let current: number|null = mem[char]
        mem[ch] = (current) ? current+1 : 1
    }
    for (let [i, ch] of str.split('').entries()) {
        if (mem[ch] == 1) {
            return i
        }
    }
    return -1
}

#Challenge

Source	Language	Runtime
DailyByte	typescript	\(\mathcal{O}(n)\)

find the first unique character in a string. A character is unique if it occurs only once in the entire string.

#Solution

count how many times each character occurs in the string, then go through it in order and return the first character which occurs only once.

#Test Cases

firstUniqueChar("abcabd") // 2
firstUniqueChar("thedailybyte") // 1
firstUniqueChar("developer") // 0