2345. Finding the Number of Visible Mountains

class Solution:
    def visibleMountains(self, peaks: List[List[int]]) -> int:
        arr = [(x - y, x + y) for x, y in peaks]
        cnt = Counter(arr)
        arr.sort(key=lambda x: (x[0], -x[1]))
        res, cur = 0, -inf
        for l, r in arr:
            if r <= cur:
                continue
            cur = r
            if cnt[(l, r)] == 1:
                res += 1
        return res