624. Maximum Distance in Arrays

Given m arrays, and each array is sorted in ascending order. Now you can pick up two integers from two different arrays (each array picks one) and calculate the distance. We define the distance between two integers a and b to be their absolute difference |a-b|. Your task is to find the maximum distance.

Example 1:

Input: 
[[1,2,3],
 [4,5],
 [1,2,3]]
Output: 4
Explanation: 
One way to reach the maximum distance 4 is to pick 1 in the first or third array and pick 5 in the second array.

Note:

1. Each given array will have at least 1 number. There will be at least two non-empty arrays.

2. The total number of the integers in all the m arrays will be in the range of [2, 10000].

3. The integers in the m arrays will be in the range of [-10000, 10000].

用curMax和curMin紀錄當前最大和最小值。主要每次res都要比較當前最小值和新讀進來的array的最大值，以及當前最大值和新讀進來的array最小值差，做比較。

int maxDistance(vector<vector<int>>& arrays) { // time: O(n); space: (1)
    int res = INT_MIN, curMax = arrays[0].back(), curMin = arrays[0].front();
    for (int i = 1; i < arrays.size(); ++i) {
        res = max({res, abs(arrays[i].front() - curMax), abs(arrays[i].back() - curMin)});
        curMax = max(curMax, arrays[i].back());
        curMin = min(curMin, arrays[i].front());
    }
    return res;
}