Question

405. Convert a Number to Hexadecimal

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Description

Given an integer num, return _a string representing its hexadecimal representation_. For negative integers, two’s complement method is used.

All the letters in the answer string should be lowercase characters, and there should not be any leading zeros in the answer except for the zero itself.

Note: You are not allowed to use any built-in library method to directly solve this problem.

 

Example 1:

Input: num = 26
Output: "1a"

Example 2:

Input: num = -1
Output: "ffffffff"

 

Constraints:

• -231 <= num <= 231 - 1

Solutions

Solution 1

class Solution:
  def toHex(self, num: int) -> str:
    if num == 0:
      return '0'
    chars = '0123456789abcdef'
    s = []
    for i in range(7, -1, -1):
      x = (num >> (4 * i)) & 0xF
      if s or x != 0:
        s.append(chars[x])
    return ''.join(s)

class Solution {
  public String toHex(int num) {
    if (num == 0) {
      return "0";
    }
    StringBuilder sb = new StringBuilder();
    while (num != 0) {
      int x = num & 15;
      if (x < 10) {
        sb.append(x);
      } else {
        sb.append((char) (x - 10 + 'a'));
      }
      num >>>= 4;
    }
    return sb.reverse().toString();
  }
}

class Solution {
public:
  string toHex(int num) {
    if (num == 0) return "0";
    string s = "";
    for (int i = 7; i >= 0; --i) {
      int x = (num >> (4 * i)) & 0xf;
      if (s.size() > 0 || x != 0) {
        char c = x < 10 ? (char) (x + '0') : (char) (x - 10 + 'a');
        s += c;
      }
    }
    return s;
  }
};

func toHex(num int) string {
  if num == 0 {
    return "0"
  }
  sb := &strings.Builder{}
  for i := 7; i >= 0; i-- {
    x := num >> (4 * i) & 0xf
    if x > 0 || sb.Len() > 0 {
      var c byte
      if x < 10 {
        c = '0' + byte(x)
      } else {
        c = 'a' + byte(x-10)
      }
      sb.WriteByte(c)
    }
  }
  return sb.String()
}

Solution 2

class Solution {
  public String toHex(int num) {
    if (num == 0) {
      return "0";
    }
    StringBuilder sb = new StringBuilder();
    for (int i = 7; i >= 0; --i) {
      int x = (num >> (4 * i)) & 0xf;
      if (sb.length() > 0 || x != 0) {
        char c = x < 10 ? (char) (x + '0') : (char) (x - 10 + 'a');
        sb.append(c);
      }
    }
    return sb.toString();
  }
}