Topcoder SRM 639 div 2 500 problem.

If I solve this problem I sholud know find N

ex) 1+2+3+5... +N = 5050

n*(n+1)/2 = 5050

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package srm639; /** * n(n+1)/2 = x 1+2+3+4+5+N * @author ddavid * */ public class AliceGameEasy { public static void main(String args[]){ AliceGameEasy age= new AliceGameEasy(); System.out.println(age.findMinimumValue(10, 0)); System.out.println(age.findMinimumValue(932599670050l, 67400241741l)); } public long findMinimumValue(long x, long y){ long sqrt = (long)Math.sqrt((x+y) *2); if(sqrt *(sqrt +1) != (x+y) *2){ return -1l; } long sum =0l; int cnt =0; while(sum < x){ sum += sqrt; sqrt--; cnt++; } return cnt; } }