504. septenary number

base-7

Title Description
Given an integer, converted to binary 7, and outputs a string.

Example 1:

Input: 100
Output: "202"

Example 2:

Input: -7
Output: "-10"
NOTE: input range is [-1e7, 1e7].

Code

public class Solution {
	public String convertToBase7(int num){
		boolean isNegative = false;
		int weight = 1;
		StringBuilder sb = new StringBuilder();
		String res;
		
		//若为负数，转为正数处理
		if(num<0){
			isNegative = true;
			num = -num;
		}else if(num == 0){
			return new String("0");
		}
		
		//确定数量级
		while(true){
			if(num>=weight && num<weight*7){
				break;
			}else{
				weight *= 7;
			}
		}
		
		//若为负数，先append一个负号
		if(isNegative){
			sb.append("-");
		}
		while(weight>=1){
			if(num>=weight){
				int curr = 0;
				for(int i=1;i<7;i++){
					if(num>=weight*i && num<weight*(i+1)){
						curr = i;
						num -= weight*i;
						break;
					}
				}
				sb.append(curr);
			}else{
				sb.append(0);
			}
			weight /= 7;
		}
		
		res = sb.toString();
		return res;
	}
}

Think
this question is not difficult, but judge for various boundary conditions should be fine, for example, is greater than or equal greater than, in the face of a number of test cases, wrong section of the opening and closing may cause can not pass.

Performance