525. Contiguous Array

Medium (Trung bình) C++ 🔗 Xem trên LeetCode

📋 Đề Bài

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.

🧠 Thuật Toán & Kỹ Thuật

Hash Table (Bảng băm)
⏱️ Thời gian O(n)
💾 Không gian O(n)

💻 Lời Giải

C++ 0525-contiguous-array.cpp 
class Solution {
public:
    int findMaxLength(vector<int>& nums) {
        unordered_map<int, int> um;
        int line = 0, ans = 0;
        const int n = nums.size();
        
        um[0] = -1;
        
        for (int i = 0; i < n; ++i) {
            line += nums[i] == 1 ? -1 : 1;
            
            if (um.count(line)) {
                ans = max(ans, i - um[line]);
            }
            else {
                um[line] = i;
            }
        }
        
        return ans;
    }
};