754. Reach a Number

You are standing at position 0 on an infinite number line. There is a destination at position target.

You can make some number of moves numMoves so that:

• On each move, you can either go left or right.
• During the ith move (starting from i == 1 to i == numMoves), you take i steps in the chosen direction.

Given the integer target, return the minimum number of moves required (i.e., the minimum numMoves) to reach the destination.

class Solution {
public:
    int reachNumber(int target) {
        target = abs(target);
        long long n = ceil((-1.0 + sqrt(1+8.0*target)) / 2);
        long long sum = n * (n+1) / 2;
        if (sum == target) return n;
        long long diff = sum - target;
        if (!(diff&1)) return n;
        
        return n + (n & 1 ? 2 : 1);
        
    }
};