Easy Python Solution
Intuition\n Describe your first thoughts on how to solve this problem. \n\n# Approach\n Describe your approach to solving the problem. \n\n# Complexity\n- Time 
# Intuition\n<!-- Describe your first thoughts on how to solve this problem. -->\n\n# Approach\n<!-- Describe your approach to solving the problem. -->\n\n# Complexity\n- Time complexity:\n<!-- Add your time complexity here, e.g. $$O(n)$$ -->\n\n- Space complexity:\n<!-- Add your space complexity here, e.g. $$O(n)$$ -->\n\n# Code\n```\nclass Solution:\n       def countOfPairs(self, nums: List[int]) -> int:        \n        total = nums[0] - sum(max(prev - cur, 0) for prev, cur in itertools.pairwise(nums))        \n        return math.comb(len(nums) + total, total) % (10 ** 9 + 7) if total >= 0 else 0\n        \n```
['Python3']