Input: [1,0,0,0,1,0,1]
Output: 2
Explanation: 
If Alex sits in the second open seat (seats[2]), then the closest person has distance 2.
If Alex sits in any other open seat, the closest person has distance 1.
Thus, the maximum distance to the closest person is 2.

Example 2:

Input: [1,0,0,0]
Output: 3
Explanation: 
If Alex sits in the last seat, the closest person is 3 seats away.
This is the maximum distance possible, so the answer is 3.

Note:

1. 1 <= seats.length <= 20000
2. seats contains only 0s or 1s, at least one 0, and at least one 1.

Solution

Time complexity: O(n)

Space complexity: O(1)

// Author: Huahua
// Running time: 15 ms
class Solution {
public:
  int maxDistToClosest(vector<int>& seats) {
    int n = seats.size();
    int prev = -1;
    int ans = 0;
    for (int i = 0; i <= n; ++i) {
      if (i == n) ans = max(ans, n - prev - 1);
      else if (seats[i]) {
        if (prev == -1) ans = i;
        else ans = max(ans, (i - prev) / 2);
        prev = i;
      }
    }
    return ans;
  }
};