题目

Your task is to construct a building which will be a pile of n cubes. The cube at the bottom will have a volume of n^3, the cube above will have volume of (n-1)^3 and so on until the top which will have a volume of 1^3.

You are given the total volume m of the building. Being given m can you find the number n of cubes you will have to build?

The parameter of the function findNb (find_nb, find-nb, findNb) will be an integer m and you have to return the integer n such as n^3 + (n-1)^3 + … + 1^3 = m if such a n exists or -1 if there is no such n.

Example

findNb(1071225) --> 45
findNb(91716553919377) --> -1

mov rdi, 1071225
call find_nb            ; rax <-- 45
mov rdi, 91716553919377
call find_nb            ; rax <-- -1

代码

public class ASum { 
    public static long findNb(long m) {
    long sum=0;
    int n=1;
        while(true){
      sum+=(long)System.Math.Pow(n,3);
      if(sum==m) return n;
      if(sum>m) return -1;
      ++n;
    }
    }   
}