Longest Substring Without Repeating Characters（Time Limit Exceeded）

问题

Given a string, find the length of the longest substring without repeating characters.

测试用例

Given "abcabcbb", the answer is "abc", which the length is 3.

Given "bbbbb", the answer is "b", with the length of 1.

Given "pwwkew", the answer is "wke", with the length of 3. Note that the answer must be a substring, "pwke" is a subsequence and not a substring.

我的代码（Time Limit Exceeded）

func lengthOfLongestSubstring(s string) int {
    var maxLength int
    var tmpString string
    maxLength = 0
    
    lengthOfString := len(s)
    //fmt.Println(lengthOfString)
    
    for i := 0; i < lengthOfString; i++{
        for j:= i + 1; j <= lengthOfString; j++{
            if j == lengthOfString {
                tmpString = s[i : ]
            }else{
                tmpString = s[i : j]
            }
            //fmt.Println(tmpString, j - i)
            if checkRepeatingChar(tmpString) && (j - i) > maxLength{
                maxLength = j - i
            }
        }
    }
    
    return maxLength
}

func checkRepeatingChar(s string) bool{
    referenceOfs := s
    
    for i := 0; i < len(s); i++{
        for j := 0; j < len(s); j++{
            //fmt.Println(s[i], referenceOfs[j])
            if i == j {
                continue
            }else if s[i] == referenceOfs[j]{
                return false
            }
        }
    }
    
    return true
}

我的代码（Accepted）