525. Contiguous Array

Problem

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

  Example 1:

Input: nums = [0,1]
Output: 2
Explanation: [0, 1] is the longest contiguous subarray with an equal number of 0 and 1.

Example 2:

Input: nums = [0,1,0]
Output: 2
Explanation: [0, 1] (or [1, 0]) is a longest contiguous subarray with equal number of 0 and 1.

  Constraints:

• 1 <= nums.length <= 10^5

• nums[i] is either 0 or 1.

Solution (Java)

class Solution {
    public int findMaxLength(int[] nums) {
        for (int i = 0; i < nums.length; i++) {
            if (nums[i] == 0) {
                nums[i] = -1;
            }
        }
        HashMap<Integer, Integer> map = new HashMap<>();
        map.put(0, -1);
        int ps = 0;
        int len = 0;
        for (int i = 0; i < nums.length; i++) {
            ps += nums[i];
            if (!map.containsKey(ps)) {
                map.put(ps, i);
            } else {
                len = Math.max(len, i - map.get(ps));
            }
        }
        return len;
    }
}

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).