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434. Number of Segments in a String

Description

Given a string s, return the number of segments in the string.

A segment is defined to be a contiguous sequence of non-space characters.

 

Example 1:

Input: s = "Hello, my name is John"
Output: 5
Explanation: The five segments are ["Hello,", "my", "name", "is", "John"]

Example 2:

Input: s = "Hello"
Output: 1

 

Constraints:

  • 0 <= s.length <= 300
  • s consists of lowercase and uppercase English letters, digits, or one of the following characters "!@#$%^&*()_+-=',.:".
  • The only space character in s is ' '.

Solutions

Solution 1: String Splitting

Thinking

Segments are blank-separated. A hand-written scan must handle leading, trailing, and repeated spaces. \(\texttt{split}\) already drops empty pieces, so its length is the answer.

The library walk is a fine first solution.

We split the string \(\textit{s}\) by spaces and then count the number of non-empty words.

The time complexity is \(O(n)\), and the space complexity is \(O(n)\), where \(n\) is the length of the string \(\textit{s}\).

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class Solution:
    def countSegments(self, s: str) -> int:
        return len(s.split())

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class Solution {
    public int countSegments(String s) {
        int ans = 0;
        for (String t : s.split(" ")) {
            if (!"".equals(t)) {
                ++ans;
            }
        }
        return ans;
    }
}

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class Solution {
public:
    int countSegments(string s) {
        int ans = 0;
        istringstream ss(s);
        while (ss >> s) ++ans;
        return ans;
    }
};

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func countSegments(s string) int {
    ans := 0
    for _, t := range strings.Split(s, " ") {
        if len(t) > 0 {
            ans++
        }
    }
    return ans
}

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function countSegments(s: string): number {
    return s.split(/\s+/).filter(Boolean).length;
}

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class Solution {
    /**
     * @param String $s
     * @return Integer
     */
    function countSegments($s) {
        $arr = explode(' ', $s);
        $cnt = 0;
        for ($i = 0; $i < count($arr); $i++) {
            if (strlen($arr[$i]) != 0) {
                $cnt++;
            }
        }
        return $cnt;
    }
}

Solution 2: Simulation

Thinking

Solution 1 allocates the list of words. Counting only, a new segment starts at a non-space whose previous character is a space (or the first index). Extra memory becomes \(O(1)\).

We can also directly traverse each character \(\text{s[i]}\) in the string. If \(\text{s[i]}\) is not a space and \(\text{s[i-1]}\) is a space or \(i = 0\), then \(\text{s[i]}\) marks the beginning of a new word, and we increment the answer by one.

After the traversal, we return the answer.

The time complexity is \(O(n)\), where \(n\) is the length of the string \(\textit{s}\). The space complexity is \(O(1)\).

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class Solution:
    def countSegments(self, s: str) -> int:
        ans = 0
        for i, c in enumerate(s):
            if c != ' ' and (i == 0 or s[i - 1] == ' '):
                ans += 1
        return ans

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class Solution {
    public int countSegments(String s) {
        int ans = 0;
        for (int i = 0; i < s.length(); ++i) {
            if (s.charAt(i) != ' ' && (i == 0 || s.charAt(i - 1) == ' ')) {
                ++ans;
            }
        }
        return ans;
    }
}

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class Solution {
public:
    int countSegments(string s) {
        int ans = 0;
        for (int i = 0; i < s.size(); ++i) {
            if (s[i] != ' ' && (i == 0 || s[i - 1] == ' ')) {
                ++ans;
            }
        }
        return ans;
    }
};

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func countSegments(s string) int {
    ans := 0
    for i, c := range s {
        if c != ' ' && (i == 0 || s[i-1] == ' ') {
            ans++
        }
    }
    return ans
}

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function countSegments(s: string): number {
    let ans = 0;
    for (let i = 0; i < s.length; i++) {
        let c = s[i];
        if (c !== ' ' && (i === 0 || s[i - 1] === ' ')) {
            ans++;
        }
    }
    return ans;
}

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class Solution {
    /**
     * @param String $s
     * @return Integer
     */
    function countSegments($s) {
        $ans = 0;
        $n = strlen($s);
        for ($i = 0; $i < $n; $i++) {
            $c = $s[$i];
            if ($c !== ' ' && ($i === 0 || $s[$i - 1] === ' ')) {
                $ans++;
            }
        }
        return $ans;
    }
}

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