lc88. Merge Sorted Array

2022-03-01 373 words 2 minutes

Contents

You are given two integer arrays nums1 and nums2, sorted in non-decreasing order, and two integers m and n, representing the number of elements in nums1 and nums2 respectively.

Merge nums1 and nums2 into a single array sorted in non-decreasing order.

The final sorted array should not be returned by the function, but instead be stored inside the array nums1. To accommodate this, nums1 has a length of m + n, where the first m elements denote the elements that should be merged, and the last n elements are set to 0 and should be ignored. nums2 has a length of n.

Example 1:

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Input: nums1 = [1,2,3,0,0,0], m = 3, nums2 = [2,5,6], n = 3
Output: [1,2,2,3,5,6]
Explanation: The arrays we are merging are [1,2,3] and [2,5,6].
The result of the merge is [1,2,2,3,5,6] with the underlined elements coming from nums1.

Example 2:

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Input: nums1 = [1], m = 1, nums2 = [], n = 0
Output: [1]
Explanation: The arrays we are merging are [1] and [].
The result of the merge is [1].

Example 3:

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Input: nums1 = [0], m = 0, nums2 = [1], n = 1
Output: [1]
Explanation: The arrays we are merging are [] and [1].
The result of the merge is [1].
Note that because m = 0, there are no elements in nums1. The 0 is only there to ensure the merge result can fit in nums1.

Constraints:

nums1.length == m + n
nums2.length == n
0 <= m, n <= 200
1 <= m + n <= 200
-109 <= nums1[i], nums2[j] <= 109

Follow up: Can you come up with an algorithm that runs in O(m + n) time?

思路

由于nums1的后序数字全为0，并且nums1和nums2都是以升序排列，所以我们可以把两个数组从大到小依次比较，然后插入num1。因为num1和num2中的数字只会遍历一次，因此最终的时间复杂度是O(m+n)。

Answer

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class Solution(object):
    def merge(self, nums1, m, nums2, n):
        """
        :type nums1: List[int]
        :type m: int
        :type nums2: List[int]
        :type n: int
        :rtype: None Do not return anything, modify nums1 in-place instead.
        """
        insert=-1
        m,n=m-1,n-1
        while m>=0 and n>=0:
            if nums1[m]>nums2[n]:
                nums1[m],nums1[insert]=nums1[insert],nums1[m]
                m-=1
            elif nums1[m]<=nums2[n]:
                nums1[insert]=nums2[n]
                n-=1
            insert-=1
        while n>=0:
            nums1[insert]=nums2[n]
            n-=1
            insert-=1
            