LeetCode1556. Thousand separated number

1556. Thousands of separators

Give you an integer n, Please add points every three （ namely “.” Symbol ） As a thousand separator , And return the result in string format .

Example 1：

 Input ：n = 987
 Output ："987"

Example 2：

 Input ：n = 1234
 Output ："1.234"

Example 3：

 Input ：n = 123456789
 Output ："123.456.789"

Example 4：

 Input ：n = 0
 Output ："0"

Tips ：

• 0 <= n < 2^31

Two 、 Method 1

simulation , Pay attention to do-while , Because there are test cases equal to 0 Of

class Solution {
    
    public String thousandSeparator(int n) {
    
        int count = 0;
        StringBuilder res = new StringBuilder();
        do {
    
            int cnt = n % 10;
            n /= 10;
            count++;
            res.append(cnt);
            if (count % 3 == 0 && n != 0) {
    
                res.append('.');
            }
        } while (n != 0);
        res.reverse();
        return res.toString();
    }
}

Complexity analysis

• Time complexity ：O(logn).
• Spatial complexity ：O(logn).