[LeetCode] Problem 754 - Reach a Number

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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

No.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.

No.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].

Code

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public int reachNumber(int target) {
    target = Math.abs(target);
    int sum = 0;
    int k = 0;

    while (sum < target) {
        k++;
        sum += k;
    }

    if ((sum - target) % 2 == 0)
        return k;
    else
        return k + 1 + (k % 2);
}