Reach a Number — LeetCode 754 Python Solution

The problem

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

Example

Input

target = 2

Output

3

Explanation

On the 1st move, we step from 0 to 1 (1 step).

Python solution

class Solution:
    def reachNumber(self, target: int) -> int:
        target = abs(target)
        s = k = 0
        while 1:
            if s >= target and (s - target) % 2 == 0:
                return k
            k += 1
            s += k

Complexity

Pattern: Monotonic Stack

Answer "what is the next greater element" for every position in one pass. LeetCode 754. Reach a Number is filed here because the reference solution below belongs to the algorithm family this hub collects, even though its LeetCode tags point elsewhere.

The monotonic stack guide has the Python template for the pattern and the 225 LeetCode problems that use it.

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