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。