src/main/java/com/fishercoder/solutions/_362.java

package com.fishercoder.solutions;

public class _362 {

    public static class Solution1 {
        public static class HitCounter {
            /**
             * Reference: https://discuss.leetcode.com/topic/48758/super-easy-design-o-1-hit-o-s-gethits-no-fancy-data-structure-is-needed,
             * I added one more field k to make it more generic.
             * It basically maintains a window of size 300, use modular to update the index.
             */
            private int[] times;
            private int[] hits;
            private int k;

            public HitCounter() {
                k = 300;
                times = new int[k];
                hits = new int[k];
            }

            public void hit(int timestamp) {
                int index = timestamp % k;
                if (times[index] != timestamp) {
                    times[index] = timestamp;
                    hits[index] = 1;
                } else {
                    hits[index]++;
                }
            }

            public int getHits(int timestamp) {
                int total = 0;
                for (int i = 0; i < k; i++) {
                    if (timestamp - times[i] < k) {
                        total += hits[i];
                    }
                }
                return total;
            }
        }
    }
}