For example:

A -> 1
B -> 2
C -> 3
...
Z -> 26
AA -> 27
AB -> 28 
...

Example 1:

Input: columnNumber = 1
Output: "A"

Example 2:

Input: columnNumber = 28
Output: "AB"

Example 3:

Input: columnNumber = 701
Output: "ZY"

Example 4:

Input: columnNumber = 2147483647
Output: "FXSHRXW"

Constraints:

• 1 <= columnNumber <= 231 - 1

Solution: Base conversion

Time complexity: O(logn)
Space complexity: O(logn)

// Author: Huahua
class Solution {
public:
  string convertToTitle(int n) {
    string ans;
    do {
      n--;
      ans += 'A' + (char)(n % 26);
      n /= 26;
    } while (n);
    reverse(begin(ans), end(ans));
    return ans;
  }
};

Related Problems

• 花花酱 LeetCode 171. Excel Sheet Column Number

The post 花花酱 LeetCode 168. Excel Sheet Column Title appeared first on Huahua's Tech Road.

After converting, each digit should be interpreted as a base 10 number, and the sum should be returned in base 10.

Example 1:

Input: n = 34, k = 6
Output: 9
Explanation: 34 (base 10) expressed in base 6 is 54. 5 + 4 = 9.

Example 2:

Input: n = 10, k = 10
Output: 1
Explanation: n is already in base 10. 1 + 0 = 1.

Constraints:

• 1 <= n <= 100
• 2 <= k <= 10

Solution: Base Conversion

Time complexity: O(logn)
Space complexity: O(1)

// Author: Huahua
class Solution {
public:
  int sumBase(int n, int k) {
    int ans = 0;
    while (n) {
      ans += n % k;
      n /= k;
    }
    return ans;
  }
};

The post 花花酱 LeetCode 1837. Sum of Digits in Base K appeared first on Huahua's Tech Road.

Problem

Given an integer, return its base 7 string representation.

Example 1:

Input: 100
Output: "202"

Example 2:

Input: -7
Output: "-10"

Note: The input will be in range of [-1e7, 1e7].

Solution: Simulation

Time complexity: O(logn)

Space complexity: O(logn)

// Author: Huahua
// Running time: 4 ms
class Solution {
public:
  string convertToBase7(int num) {
    bool is_nagetive = num<0;
    num = abs(num);
    string ans;
    do {
        ans += ('0' + (num % 7));
        num /= 7;
    } while (num > 0);
    
    if (is_nagetive)
        ans += "-";
    
    reverse(begin(ans), end(ans));
    
    return ans;
  }
};

The post 花花酱 LeetCode 504. Base 7 appeared first on Huahua's Tech Road.