题目：

题解：

class Solution {
public:string toHex(int num) {if (num == 0) {return "0";}string sb;for (int i = 7; i >= 0; i --) {int val = (num >> (4 * i)) & 0xf;if (sb.length() > 0 || val > 0) {char digit = val < 10 ? (char) ('0' + val) : (char) ('a' + val - 10);sb.push_back(digit);}}return sb;}
};