LeetCode 3178: Find the Child Who Has the Ball After K Seconds Solution

Master LeetCode problem 3178 (Find the Child Who Has the Ball After K Seconds), a easy challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

3178. Find the Child Who Has the Ball After K Seconds

Easy

Math Simulation

Problem Explanation

Explanation

To solve this problem, we can simulate the passing of the ball among the children. We need to keep track of which child currently has the ball and the direction in which it is being passed. We iterate through seconds passing the ball to the next child and updating the direction if the ball reaches either end of the line.

Initialize variables ballHolder to 0 (representing child 0 holding the ball), direction to 1 (representing passing towards the right), and remainingSec to k.
While remainingSec is greater than 0:
- If direction is 1 and ballHolder is n-1, update direction to -1 (passing towards the left).
- If direction is -1 and ballHolder is 0, update direction to 1 (passing towards the right).
- Update ballHolder to the next child based on the current direction.
- Decrement remainingSec by 1.
Return the final ballHolder.

The time complexity of this solution is O(k) as we iterate through k seconds, and the space complexity is O(1) as we only use a constant amount of extra space.

Solution Code

class Solution {
    public int findTheBall(int n, int k) {
        int ballHolder = 0;
        int direction = 1;
        int remainingSec = k;

        while (remainingSec > 0) {
            if (direction == 1 && ballHolder == n - 1) {
                direction = -1;
            } else if (direction == -1 && ballHolder == 0) {
                direction = 1;
            }
            ballHolder += direction;
            remainingSec--;
        }

        return ballHolder;
    }
}

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