題意：把整數(shù)轉(zhuǎn)換成十六進(jìn)制數(shù)

思路：把數(shù)字和15于8次，每次把于出來(lái)的十六進(jìn)制字符加入結(jié)果，并把temp右移4位，如果中間遇到temp＝＝0break，最后把字符串翻轉(zhuǎn)并轉(zhuǎn)換成字符串

思想：位運(yùn)算

復(fù)雜度：時(shí)間O（n)，空間O(1)

class Solution {
    public String toHex(int num) {
        String[] m = {"0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "a", "b", "c", "d", "e", "f"};
        
        int temp = num;
        
        StringBuilder sb = new StringBuilder();
        while(sb.length() < 8) {
            int cur = temp & 15;
            sb.append(m[cur]);
            temp = temp >> 4;
            if(temp == 0)
                break;
        }
        
        return sb.reverse().toString();
    }
}