## Monday, September 26, 2016

### LeetCode 405 - Convert a Number to Hexadecimal

Given an integer, write an algorithm to convert it to hexadecimal. For negative integer, two’s complement method is used.
Note:
1. All letters in hexadecimal (`a-f`) must be in lowercase.
2. The hexadecimal string must not contain extra leading `0`s. If the number is zero, it is represented by a single zero character `'0'`; otherwise, the first character in the hexadecimal string will not be the zero character.
3. The given number is guaranteed to fit within the range of a 32-bit signed integer.
4. You must not use any method provided by the library which converts/formats the number to hex directly.
Example 1:
```Input:
26

Output:
"1a"
```
Example 2:

```Input:
-1

Output:
"ffffffff"
```
https://discuss.leetcode.com/topic/60365/simple-java-solution-with-comment
``````Basic idea: each time we take a look at the last four digits of
binary verion of the input, and maps that to a hex char
shift the input to the right by 4 bits, do it again
until input becomes 0.
char[] map = {'0','1','2','3','4','5','6','7','8','9','a','b','c','d','e','f'};

public String toHex(int num) {
if(num == 0) return "0";
String result = "";
while(num != 0){
result = map[(num & 15)] + result;
num = (num >>> 4);
}
return result;
}``````
https://discuss.leetcode.com/topic/60414/java-solution
``````  public String toHex(int dec) {
if (dec == 0) return "0";
StringBuilder res = new StringBuilder();

while (dec != 0) {
int digit = dec & 0xf;
res.append(digit < 10 ? (char)(digit + '0') : (char)(digit - 10 + 'a'));
dec >>>= 4;
}

return res.reverse().toString();
}``````
https://discuss.leetcode.com/topic/60365/simple-java-solution-with-comment/3
StringBuilder may be used here.
``````    public String toHex(int num) {
StringBuilder sb = new StringBuilder();
do {
int n = num & 0xf;
n += n < 0xa ? '0' : 'a' - 10;
sb.append((char)n);
} while ((num >>>= 4) != 0);
return sb.reverse().toString();
}``````
X. DFS
https://discuss.leetcode.com/topic/60419/java-solution-num-0xffffffffl-to-long
``````    public String toHex(int num) {
return num == 0 ? "0" : toHex(num & 0xffffffffL);
}

public String toHex(long num) {
return num < 16 ? hexdigit(num) : toHex(num / 16) + hexdigit(num % 16);
}

private String hexdigit(long num) {
assert num < 16;
return num < 10 ? Character.toString((char)(num + '0')) : Character.toString((char)(num - 10 + 'a'));
}``````