Finding the largest subarray with equal number of 0's and 1's

Question

So, I have an array containing only 0\'s and 1\'s. I have to find out the largest subarray containing equal number of 0\'s and 1\'s. One can be a naive approach have complex

Answer 1

Algorithm

We make use of a HashMap map to store the entries in the form of (index,count). We make an entry for a count in the map whenever the count is encountered first, and later on use the corresponding index to find the length of the largest subarray with equal no. of zeros and ones when the same count is encountered again.

public class Solution {

    public int findMaxLength(int[] nums) {
        Map map = new HashMap<>();
        map.put(0, -1);
        int maxlen = 0, count = 0;
        for (int i = 0; i < nums.length; i++) {
            count = count + (nums[i] == 1 ? 1 : -1);
            if (map.containsKey(count)) {
                maxlen = Math.max(maxlen, i - map.get(count));
            } else {
                map.put(count, i);
            }
        }
        return maxlen;
    }
}





Time complexity : O(n). The entire array is traversed only once.

Space complexity : O(n). Maximum size of the HashMap map will be n, if all the elements are either 1 or 0.