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# Create by Hua on 5/20/22
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"""
You are given a 0-indexed integer array nums. An index i is part of a hill in nums if the closest non-equal neighbors of i are smaller than nums[i]. Similarly, an index i is part of a valley in nums if the closest non-equal neighbors of i are larger than nums[i]. Adjacent indices i and j are part of the same hill or valley if nums[i] == nums[j].

Note that for an index to be part of a hill or valley, it must have a non-equal neighbor on both the left and right of the index.

Return the number of hills and valleys in nums.



Example 1:

Input: nums = [2,4,1,1,6,5]
Output: 3
Explanation:
At index 0: There is no non-equal neighbor of 2 on the left, so index 0 is neither a hill nor a valley.
At index 1: The closest non-equal neighbors of 4 are 2 and 1. Since 4 > 2 and 4 > 1, index 1 is a hill.
At index 2: The closest non-equal neighbors of 1 are 4 and 6. Since 1 < 4 and 1 < 6, index 2 is a valley.
At index 3: The closest non-equal neighbors of 1 are 4 and 6. Since 1 < 4 and 1 < 6, index 3 is a valley, but note that it is part of the same valley as index 2.
At index 4: The closest non-equal neighbors of 6 are 1 and 5. Since 6 > 1 and 6 > 5, index 4 is a hill.
At index 5: There is no non-equal neighbor of 5 on the right, so index 5 is neither a hill nor a valley.
There are 3 hills and valleys so we return 3.
Example 2:

Input: nums = [6,6,5,5,4,1]
Output: 0
Explanation:
At index 0: There is no non-equal neighbor of 6 on the left, so index 0 is neither a hill nor a valley.
At index 1: There is no non-equal neighbor of 6 on the left, so index 1 is neither a hill nor a valley.
At index 2: The closest non-equal neighbors of 5 are 6 and 4. Since 5 < 6 and 5 > 4, index 2 is neither a hill nor a valley.
At index 3: The closest non-equal neighbors of 5 are 6 and 4. Since 5 < 6 and 5 > 4, index 3 is neither a hill nor a valley.
At index 4: The closest non-equal neighbors of 4 are 5 and 1. Since 4 < 5 and 4 > 1, index 4 is neither a hill nor a valley.
At index 5: There is no non-equal neighbor of 1 on the right, so index 5 is neither a hill nor a valley.
There are 0 hills and valleys so we return 0.


Constraints:

3 <= nums.length <= 100
1 <= nums[i] <= 100
"""


class Solution(object):
    def countHillValley(self, nums):
        """
        :type nums: List[int]
        :rtype: int

        thought: 2 pointers. need to skip equal value and check left and right
        i points the leftmost, and j points the rightmost
        05/20/2022 14:04	Accepted	39 ms	13.2 MB	python
        easy 10-20min. not very easy to get it correct.

        # concise code
         public int countHillValley(int[] a){
            int r = 0, left = a[0];
            for(int i = 1; i < a.length - 1; i++)
                if(left < a[i] && a[i] > a[i + 1] || left > a[i] && a[i] < a[i + 1]){
                    r++;
                    left = a[i];
                }
            return r;
        }

        """
        i = 1
        n = len(nums)
        # init pos
        while i < n-1 and nums[i] == nums[0]:
            i += 1

        ret = 0
        j = i
        while i < n-1 and j < n :
            if nums[i] == nums[j]:
                j += 1
            elif (nums[i-1] < nums[i] and nums[i] > nums[j]) or (nums[i-1] > nums[i] and nums[i] < nums[j]):
                ret += 1
                i = j
            else: # non-valley or hill
                i=j
        return ret
