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2414. Length of the Longest Alphabetical Continuous Substring

Description

An alphabetical continuous string is a string consisting of consecutive letters in the alphabet. In other words, it is any substring of the string "abcdefghijklmnopqrstuvwxyz".

  • For example, "abc" is an alphabetical continuous string, while "acb" and "za" are not.

Given a string s consisting of lowercase letters only, return the length of the longest alphabetical continuous substring.

 

Example 1:

Input: s = "abacaba"
Output: 2
Explanation: There are 4 distinct continuous substrings: "a", "b", "c" and "ab".
"ab" is the longest continuous substring.

Example 2:

Input: s = "abcde"
Output: 5
Explanation: "abcde" is the longest continuous substring.

 

Constraints:

  • 1 <= s.length <= 105
  • s consists of only English lowercase letters.

Solutions

Solution 1: Single Pass

We can traverse the string $s$ and use a variable $\textit{ans}$ to record the length of the longest lexicographically consecutive substring, and another variable $\textit{cnt}$ to record the length of the current consecutive substring. Initially, $\textit{ans} = \textit{cnt} = 1$.

Next, we start traversing the string $s$ from the character at index $1$. For each character $s[i]$, if $s[i] - s[i - 1] = 1$, it means the current character and the previous character are consecutive. In this case, $\textit{cnt} = \textit{cnt} + 1$, and we update $\textit{ans} = \max(\textit{ans}, \textit{cnt})$. Otherwise, it means the current character and the previous character are not consecutive, so $\textit{cnt} = 1$.

Finally, we return $\textit{ans}$.

The time complexity is $O(n)$, where $n$ is the length of the string $s$. The space complexity is $O(1)$.

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class Solution:
    def longestContinuousSubstring(self, s: str) -> int:
        ans = cnt = 1
        for x, y in pairwise(map(ord, s)):
            if y - x == 1:
                cnt += 1
                ans = max(ans, cnt)
            else:
                cnt = 1
        return ans

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class Solution {
    public int longestContinuousSubstring(String s) {
        int ans = 1, cnt = 1;
        for (int i = 1; i < s.length(); ++i) {
            if (s.charAt(i) - s.charAt(i - 1) == 1) {
                ans = Math.max(ans, ++cnt);
            } else {
                cnt = 1;
            }
        }
        return ans;
    }
}

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class Solution {
public:
    int longestContinuousSubstring(string s) {
        int ans = 1, cnt = 1;
        for (int i = 1; i < s.size(); ++i) {
            if (s[i] - s[i - 1] == 1) {
                ans = max(ans, ++cnt);
            } else {
                cnt = 1;
            }
        }
        return ans;
    }
};

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func longestContinuousSubstring(s string) int {
    ans, cnt := 1, 1
    for i := range s[1:] {
        if s[i+1]-s[i] == 1 {
            cnt++
            ans = max(ans, cnt)
        } else {
            cnt = 1
        }
    }
    return ans
}

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function longestContinuousSubstring(s: string): number {
    let [ans, cnt] = [1, 1];
    for (let i = 1; i < s.length; ++i) {
        if (s.charCodeAt(i) - s.charCodeAt(i - 1) === 1) {
            ans = Math.max(ans, ++cnt);
        } else {
            cnt = 1;
        }
    }
    return ans;
}

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impl Solution {
    pub fn longest_continuous_substring(s: String) -> i32 {
        let mut ans = 1;
        let mut cnt = 1;
        let s = s.as_bytes();
        for i in 1..s.len() {
            if s[i] - s[i - 1] == 1 {
                cnt += 1;
                ans = ans.max(cnt);
            } else {
                cnt = 1;
            }
        }
        ans
    }
}

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#define max(a, b) (((a) > (b)) ? (a) : (b))

int longestContinuousSubstring(char* s) {
    int n = strlen(s);
    int ans = 1, cnt = 1;
    for (int i = 1; i < n; ++i) {
        if (s[i] - s[i - 1] == 1) {
            ++cnt;
            ans = max(ans, cnt);
        } else {
            cnt = 1;
        }
    }
    return ans;
}

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