ContiguousArray525.java

/**
 * Given a binary array, find the maximum length of a contiguous subarray with
 * equal number of 0 and 1.
 *
 * Example 1:
 *    Input: [0,1]
 *    Output: 2
 *
 * Explanation: [0, 1] is the longest contiguous subarray with equal number of 0 and 1.
 *
 * Example 2:
 *    Input: [0,1,0]
 *    Output: 2
 *
 * Explanation: [0, 1] (or [1, 0]) is a longest contiguous subarray with equal number of 0 and 1.
 *
 * Note: The length of the given binary array will not exceed 50,000.
 *
 */


public class ContiguousArray525 {
    /**
     * https://leetcode.com/problems/contiguous-array/solution/
     */
    public int findMaxLength(int[] nums) {
        int maxlen = 0;
        for (int start = 0; start < nums.length; start++) {
            int zeroes = 0, ones = 0;
            for (int end = start; end < nums.length; end++) {
                if (nums[end] == 0) {
                    zeroes++;
                } else {
                    ones++;
                }
                if (zeroes == ones) {
                    maxlen = Math.max(maxlen, end - start + 1);
                }
            }
        }
        return maxlen;
    }

    public int findMaxLength2(int[] nums) {
        int[] arr = new int[2 * nums.length + 1];
        Arrays.fill(arr, -2);
        arr[nums.length] = -1;
        int maxlen = 0, count = 0;
        for (int i = 0; i < nums.length; i++) {
            count = count + (nums[i] == 0 ? -1 : 1);
            if (arr[count + nums.length] >= -1) {
                maxlen = Math.max(maxlen, i - arr[count + nums.length]);
            } else {
                arr[count + nums.length] = i;
            }

        }
        return maxlen;
    }

    public int findMaxLength3(int[] nums) {
        Map<Integer, Integer> 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;
    }

}