Merge Sorted Array in leetcode

Question

i saw this in https://leetcode.com/problems/merge-sorted-array/description/ and the answer in https://leetcode.com/problems/merge-sorted-array/discuss/29503/Beautiful-Python-Solution

def merge(self, nums1, m, nums2, n):
        while m > 0 and n > 0:
            if nums1[m-1] >= nums2[n-1]:
                nums1[m+n-1] = nums1[m-1]
                m -= 1
            else:
                nums1[m+n-1] = nums2[n-1]
                n -= 1
        if n > 0:
            nums1[:n] = nums2[:n]

I have two doubts:

When i want to run the code print(Solution().merge([1, 2, 3], 3, [4, 5, 6], 3)) and it just gave me an error hint IndexError: list assignment index out of range.
I don’t quite understand the methodology in the answer above.
Could someone tell me how to solve this kind of problem?

Asked By: Peter Tsung

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Source

Answer 1

The problem is here:

def merge(self, nums1, m, nums2, n):
    while m > 0 and n > 0:
        if nums1[m-1] >= nums2[n-1]:
            nums1[m+n-1] = nums1[m-1]   # nums1[m+n-1] IndexError
            m -= 1
        else:
            nums1[m+n-1] = nums2[n-1]   # Same as above
            n -= 1
    if n > 0:
        nums1[:n] = nums2[:n]

You may want to “resize” the list first to prevent index error:

def merge(self, nums1, m, nums2, n):
    nums1 += nums2
    # Or nums1 += [None] * len(nums2)

    while m > 0 and n > 0:
        if nums1[m-1] >= nums2[n-1]:
            nums1[m+n-1] = nums1[m-1] # nums1[m+n-1] IndexError
            m -= 1
        else:
            nums1[m+n-1] = nums2[n-1] # Same as above
            n -= 1
    if n > 0:
        nums1[:n] = nums2[:n]

Answered By: iBug

Answer 2

def merge_two_sorted_arrays(left: list, right: list) -> list:
    """
    Merge Sorted Array in leetcode
    Args:
        left: left array
        right: right array

    Returns: A new merged array
    """
    A = [None] * (len(left) + len(right))
    i = j = k = 0
    while i < len(left) and j < len(right):
        if left[i] < right[j]:
            A[k] = left[i]
            i += 1
        else:
            A[k] = right[j]
            j += 1
        k += 1
    while i < len(left):
        A[k] = left[i]
        i += 1
        k += 1
    while j < len(right):
        A[k] = right[j]
        j += 1
        k += 1

    return A


a = [1, 2, 2, 4]
b = [3, 5, 6, 9]

print(merge_two_sorted_arrays(a, b))

Output:

[1, 2, 2, 3, 4, 5, 6, 9]

Answered By: Soumya Ranjan Rout

Answer 3

class Solution:
    def merge(self, nums1: List[int], m: int, nums2: List[int], n: int) -> None:
        nums1[m:] = nums2
        nums1.sort()

Answered By: Сергей Протасов

Merge Sorted Array in leetcode

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