ContiguousArray.java

import java.util.HashMap;
import java.util.Map;

/*
Given a binary array nums, return the maximum length of a contiguous subarray with an equal number of 0 and 1.

Example:
Input: nums = [0,1]
Output: 2
Explanation: [0, 1] is the longest contiguous subarray with an equal number of 0 and 1.
 */
public class ContiguousArray {

    public static void main(String[] args) {
        int[] testBinaryArr = {0,0,0,1,1,1}; //6
        int[] testBinaryArr2 = {0,1,0,1,1,1}; //4

        System.out.println(findMaxLength(testBinaryArr));
        System.out.println(findMaxLength(testBinaryArr2));
    }

    private static int findMaxLength(int [] nums) {
        if(nums.length == 1) return 0;

        for(int i = 0; i < nums.length; i++) {
            if(nums[i] == 0) nums[i] = -1;
        }

        int max = 0;
        int sum = 0;
        Map<Integer, Integer> map = new HashMap<>();
        map.put(0, -1);

        for(int i = 0; i < nums.length; i++) {
            sum+=nums[i];
            if(map.containsKey(sum)) {
                int last = map.get(sum);
                max = Math.max(max, i - last);
            } else {
                map.put(sum, i);
            }
        }
        return max;
    }
}