Efficient C++ Solution


int Solution::solve(int A) {
int target = abs(A);
int sum = 0, ans = 0;
while (sum < target || (sum - target) % 2 != 0) {
sum += ans;
return ans;


Can you explain why have you used (sum - target) % 2 != 0?


Because geeksforgeeks did the same:joy::joy:


Imagine the case with 9.
If we only took positive steps, it would be 1+2+3+4=10>9.
Now, at any point(say i), if you would have taken a step backward, your sum would have been 2*i less than the sum you have if i was in positive direction.

So in case sum-2i=target, it means we have to take one negative step
This means (sum-target)=2
i i.e. (sum-target is even).

Hence you go on to the next move until the condition (sum-target==2*i) is true
This is why you check (sum-target)%2!=0 at every iteration of the loop.