leetcode 【 Merge Sorted Array 】python 实现

题目：

Given two sorted integer arrays A and B, merge B into A as one sorted array.

Note:
You may assume that A has enough space (size that is greater or equal to m + n) to hold additional elements from B. The number of elements initialized in A and B are m and nrespectively.

代码：oj测试通过 Runtime: 58 ms

 class Solution:
     # @param A  a list of integers
     # @param m  an integer, length of A
     # @param B  a list of integers
     # @param n  an integer, length of B
     # @return nothing
     def merge(self, A, m, B, n):

         index_total = m + n - 1
         indexA = m-1
         indexB = n-1

         while indexA >= 0 and indexB >= 0 :
             if A[indexA] > B[indexB]:
                 A[index_total] = A[indexA]
                 indexA -= 1
             else:
                 A[index_total] = B[indexB]
                 indexB -= 1
             index_total -= 1

         if indexA >= 0:
             while indexA >= 0:
                 A[index_total] = A[indexA]
                 indexA -= 1
                 index_total -= 1
         else:
             while indexB >= 0:
                 A[index_total] = B[indexB]
                 indexB -= 1
                 index_total -= 1

思路：

采用最基础的两路归并思想。针对A B两个数组维护两个指针。

这里用到一个技巧是：从后往前遍历。

这样可以不用再开辟一个m+n空间的数组。