LeetCode - Reach a Number

Question Definition

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

On each move, you can either go left or right. During the n-th move (starting from 1), you take n steps.

Return the minimum number of steps required to reach the destination.

Example 1:

Input: target = 3
Output: 2
Explanation:
On the first move we step from 0 to 1.
On the second step we step from 1 to 3.

Example 2:

Input: target = 2
Output: 3
Explanation:
On the first move we step from 0 to 1.
On the second move we step  from 1 to -1.
On the third move we step from -1 to 2.

Note:

• target will be a non-zero integer in the range [-10^9, 10^9].

  Java Solution

  public int reachNumber(int target) {
    target = Math.abs(target);
    int res = 0, sum = 0;
    while (sum < target || (sum - target) % 2 == 1) {
        ++res;
        sum += res;
    }
    return res;
  }