Write a mode method in Java to find the most frequently occurring element in an array

Question

The question goes:

Write a method called mode that returns the most frequently occurring element of an array of integers. Assume that the array has at le

Answer 1

You should be able to do this in N operations, meaning in just one pass, O(n) time.

Use a map or int[] (if the problem is only for ints) to increment the counters, and also use a variable that keeps the key which has the max count seen. Everytime you increment a counter, ask what the value is and compare it to the key you used last, if the value is bigger update the key.

public class Mode {
public static int mode(final int[] n) {
    int maxKey = 0;
    int maxCounts = 0;

    int[] counts = new int[n.length];

    for (int i=0; i < n.length; i++) {
        counts[n[i]]++;
        if (maxCounts < counts[n[i]]) {
            maxCounts = counts[n[i]];
            maxKey = n[i];
        }
    }
    return maxKey;
}

public static void main(String[] args) {
    int[] n = new int[] { 3,7,4,1,3,8,9,3,7,1 };
    System.out.println(mode(n));
}
}