504-7进制数

LeetCode 504. Base 7

LeetCode-504

Given an integer num, return a string of its base 7 representation.

Example 1:

Input: num = 100
Output: "202"

Example 2:

Input: num = -7
Output: "-10"

method 1: 模拟

注意进制转换的写法
int如何转换为char，也可以用to_string()转换为string

string convertToBase7(int num) {
    if (num == 0) return "0";
    int x = num > 0 ? num : -num;
    string ret;
    while (x) {
        ret = char('0' + x % 7) + ret;
        x /= 7;
    }
    if (num < 0) ret = '-' + ret;
    return ret;
}

method 2: 递归

• 小于0，加个负号，再递归处理相反数
• 小于7，直接返回整数转成的字符串
• 大于7，除以7部分继续递归，模以7部分转成字符串

string convertToBase7(int num) {
    if (num < 0) return "-" + convertToBase7(-num);
    if (num < 7) return to_string(num);
    return convertToBase7(num / 7) + to_string(num % 7);
}