Easy to understand Python solution

  • 1

    The idea is:

    1. we ignore duplicates in all points with same y values and only save once for duplicates (e.g., for [16,1], [16,1], [16,1], we only save [16,1] once to the dictionary).
    2. we calculate an average x value for all saved points
    3. for all points with same y values, set two pointers (from left and right) to check whether the point pair has the same distance to the average x value.


    def isReflected(self, points):
        if (not points):
            return True
        dic = {}
        sumx = 0
        lenwithoutdup = 0
        for point in points:
            if point[1] not in dic:
                dic[point[1]] = {point[0]}
                sumx += point[0]
                lenwithoutdup += 1
                if point[0] not in dic[point[1]]:
                    sumx += point[0]
                    lenwithoutdup += 1
        #print sumx, lenwithoutdup
        avgx = float(sumx)/lenwithoutdup
        for item in dic:
            lst = list(dic[item])
            i, j = 0, len(lst)-1  # two pointers
            while i <= j:
                #print lst[i], avgx, lst[j]
                if lst[i] - avgx != avgx - lst[j]:
                    return False
                i += 1
                j -= 1
        return True

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