Create Target Array in the Given Order LeetCode solution in Python

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class Solution:
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    def createTargetArray(self, nums, index):
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        def merge(arr, low, mid, high):
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            L, R = arr[low : mid + 1], arr[mid + 1 : high + 1]
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            i = j = 0
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            k = low
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            while i < len(L) and j < len(R):
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                if L[i][0] + j >= R[j][0]:
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                    arr[k] = R[j]
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                    j += 1
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                else:
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                    L[i][0] += j
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                    arr[k] = L[i]
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                    i += 1
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                k += 1
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            while i < len(L):
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                L[i][0] += j
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                arr[k] = L[i]
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                i += 1
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                k += 1
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            while j < len(R):
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                arr[k] = R[j]
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                j += 1
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                k += 1
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        def mergeSort(arr, low, high):
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            if low < high:
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                mid = (low + high) // 2
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                mergeSort(arr, low, mid)
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                mergeSort(arr, mid + 1, high)
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                merge(arr, low, mid, high)
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        arr = [[index[i], nums[i]] for i in range(len(nums))]
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        mergeSort(arr, 0, len(nums) - 1)
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        for x in arr:
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            nums[x[0]] = x[1]
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        return nums