Question

525. Contiguous Array

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Description

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 <= 105
• nums[i] is either 0 or 1.

Solutions

Solution 1

class Solution:
  def findMaxLength(self, nums: List[int]) -> int:
    s = ans = 0
    mp = {0: -1}
    for i, v in enumerate(nums):
      s += 1 if v == 1 else -1
      if s in mp:
        ans = max(ans, i - mp[s])
      else:
        mp[s] = i
    return ans

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

class Solution {
public:
  int findMaxLength(vector<int>& nums) {
    unordered_map<int, int> mp;
    int s = 0, ans = 0;
    mp[0] = -1;
    for (int i = 0; i < nums.size(); ++i) {
      s += nums[i] == 1 ? 1 : -1;
      if (mp.count(s))
        ans = max(ans, i - mp[s]);
      else
        mp[s] = i;
    }
    return ans;
  }
};

func findMaxLength(nums []int) int {
  mp := map[int]int{0: -1}
  s, ans := 0, 0
  for i, v := range nums {
    if v == 0 {
      v = -1
    }
    s += v
    if j, ok := mp[s]; ok {
      ans = max(ans, i-j)
    } else {
      mp[s] = i
    }
  }
  return ans
}

/**
 * @param {number[]} nums
 * @return {number}
 */
var findMaxLength = function (nums) {
  const mp = new Map();
  mp.set(0, -1);
  let s = 0;
  let ans = 0;
  for (let i = 0; i < nums.length; ++i) {
    s += nums[i] == 0 ? -1 : 1;
    if (mp.has(s)) ans = Math.max(ans, i - mp.get(s));
    else mp.set(s, i);
  }
  return ans;
};