525. Contiguous Array

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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.

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解法一：summation 遇到 0 減一, 遇到 1 加一，當數組同時有兩個相同元素出現，代表這兩元素間一定有相同的 0 和 1 個數

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