Skip to content

504. Base 7

Description

Given an integer num, return a string of its base 7 representation.

 

Example 1:

Input: num = 100
Output: "202"

Example 2:

Input: num = -7
Output: "-10"

 

Constraints:

  • -107 <= num <= 107

Solutions

Solution 1

Thinking

Base-7 conversion is repeated division by \(7\). Handle \(0\) directly and convert the absolute value of a negative number, then restore the sign. Remainders come out least-significant first, so reverse before joining.

The loop runs once per digit, which is \(O(\log |num|)\).

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
class Solution:
    def convertToBase7(self, num: int) -> str:
        if num == 0:
            return '0'
        if num < 0:
            return '-' + self.convertToBase7(-num)
        ans = []
        while num:
            ans.append(str(num % 7))
            num //= 7
        return ''.join(ans[::-1])

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
class Solution {
    public String convertToBase7(int num) {
        if (num == 0) {
            return "0";
        }
        if (num < 0) {
            return "-" + convertToBase7(-num);
        }
        StringBuilder sb = new StringBuilder();
        while (num != 0) {
            sb.append(num % 7);
            num /= 7;
        }
        return sb.reverse().toString();
    }
}

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
class Solution {
public:
    string convertToBase7(int num) {
        if (num == 0) return "0";
        if (num < 0) return "-" + convertToBase7(-num);
        string ans = "";
        while (num) {
            ans = to_string(num % 7) + ans;
            num /= 7;
        }
        return ans;
    }
};

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
func convertToBase7(num int) string {
    if num == 0 {
        return "0"
    }
    if num < 0 {
        return "-" + convertToBase7(-num)
    }
    ans := []byte{}
    for num != 0 {
        ans = append([]byte{'0' + byte(num%7)}, ans...)
        num /= 7
    }
    return string(ans)
}

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
function convertToBase7(num: number): string {
    if (num == 0) {
        return '0';
    }
    let res = '';
    const isMinus = num < 0;
    if (isMinus) {
        num = -num;
    }
    while (num != 0) {
        const r = num % 7;
        res = r + res;
        num = (num - r) / 7;
    }
    return isMinus ? '-' + res : res;
}

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
impl Solution {
    pub fn convert_to_base7(mut num: i32) -> String {
        if num == 0 {
            return String::from("0");
        }
        let mut res = String::new();
        let is_minus = num < 0;
        if is_minus {
            num = -num;
        }
        while num != 0 {
            res.push_str((num % 7).to_string().as_str());
            num /= 7;
        }
        if is_minus {
            res.push('-');
        }
        res.chars().rev().collect()
    }
}

Comments