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709. To Lower Case

Description

Given a string s, return the string after replacing every uppercase letter with the same lowercase letter.

 

Example 1:

Input: s = "Hello"
Output: "hello"

Example 2:

Input: s = "here"
Output: "here"

Example 3:

Input: s = "LOVELY"
Output: "lovely"

 

Constraints:

  • 1 <= s.length <= 100
  • s consists of printable ASCII characters.

Solutions

Solution 1

Thinking

Convert uppercase letters to lowercase; \(n \le 100\). A library call works, and so does an ASCII walk.

Each uppercase letter is \(32\) below its lowercase counterpart, i.e. bit \(5\) of the code point. Bitwise-or with \(32\) lowercases it; other characters stay unchanged.

Map every character: if it is uppercase, emit \(\operatorname{ord}(c)\,|\,32\). Time \(O(n)\).

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class Solution:
    def toLowerCase(self, s: str) -> str:
        return "".join([chr(ord(c) | 32) if c.isupper() else c for c in s])

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class Solution {
    public String toLowerCase(String s) {
        char[] cs = s.toCharArray();
        for (int i = 0; i < cs.length; ++i) {
            if (cs[i] >= 'A' && cs[i] <= 'Z') {
                cs[i] |= 32;
            }
        }
        return String.valueOf(cs);
    }
}

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class Solution {
public:
    string toLowerCase(string s) {
        for (char& c : s) {
            if (c >= 'A' && c <= 'Z') {
                c |= 32;
            }
        }
        return s;
    }
};

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func toLowerCase(s string) string {
    cs := []byte(s)
    for i, c := range cs {
        if c >= 'A' && c <= 'Z' {
            cs[i] |= 32
        }
    }
    return string(cs)
}

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function toLowerCase(s: string): string {
    return s.toLowerCase();
}

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impl Solution {
    pub fn to_lower_case(s: String) -> String {
        s.to_ascii_lowercase()
    }
}

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char* toLowerCase(char* s) {
    int n = strlen(s);
    for (int i = 0; i < n; i++) {
        if (s[i] >= 'A' && s[i] <= 'Z') {
            s[i] |= 32;
        }
    }
    return s;
}

Solution 2

Thinking

Solution 1 branches on isupper. Lowercase ASCII already has bit \(5\) set, so or-ing \(32\) is a no-op there and we can apply it uniformly.

The TypeScript tab ors every character; the Rust tab still guards \(A\)–\(Z\) so non-letters are untouched. Neither version calls a locale-aware lowercasing API.

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function toLowerCase(s: string): string {
    return [...s].map(c => String.fromCharCode(c.charCodeAt(0) | 32)).join('');
}

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impl Solution {
    pub fn to_lower_case(s: String) -> String {
        s.as_bytes()
            .iter()
            .map(|&c| char::from(if c >= b'A' && c <= b'Z' { c | 32 } else { c }))
            .collect()
    }
}

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