[LeetCode] 405. Convert a Number to Hexadecimal

轉自LeetCode

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 0s. 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"

<Solution>

想法如下(參考資料)

• 每次都看最後面的 4 個 bits，將它們轉換成 hex

• 將數字右移4位，直到為0

code 如下

C++

因為 C++ 沒有 >>> 這種運算元，所以必須先轉成 unsigned int

這樣右移時，才能確保MSB都會填0

	class Solution {
	public:
	string toHex(int num) {
	if(num == 0) {
	return "0";
	}
	char map[] = {'0','1','2','3','4','5','6','7','8','9','a','b','c','d','e','f'};
	string result = "";
	unsigned int unum = num;
	while(unum != 0) {
	result = map[(unum & 15)] + result;
	unum >>= 4;
	}
	return result;
	}
	};

view raw convertNumberToHex.cpp hosted with ❤ by GitHub

Java

	class Solution {
	public String toHex(int num) {
	if(num == 0) {
	return "0";
	}
	char[] map = {'0','1','2','3','4','5','6','7','8','9','a','b','c','d','e','f'};
	String ans = "";
	while(num != 0) {
	ans = map[num & 15] + ans;
	num >>>= 4;
	}
	return ans;
	}
	}

view raw convertNumberToHex.java hosted with ❤ by GitHub