The sword refers to Offer 50. The first character that appears only once

Topic describes

Find the first character in the string s that occurs only once. If not, a single space is returned. The s contains only lowercase letters. Example:

S = “abaccdeff” return “b”

S = “return “”

A Map B Map C Map D Map

Iterate over the string directly, marking each character true the first time it occurs and false the next time it occurs. At the end of the loop, characters marked true are characters that occur once. We iterate through the string again, checking the map in order to see if it is marked true, and get the first occurrence of the character

The sample code

def firstUniqChar(self, s: str) - >str:
    map = {}
    for i in s:
        if i in map:
            map[i] = False
        else:
            map[i] = True

    for i in s:
        if map[i] == True:
            return i
            
    return ""
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