LeetCode::Merge Sorted Array C++语言

问题

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 n respectively.

分析

A数组空间够大，而且两个数组都是排序好的。这两个信息提示我们的输出是A[m+n]，所以我们可以直接从后往前，由大到小填充。

代码：能用？：就别用if else 效率真的有差距的

class Solution {
public:
    void merge(int A[], int m, int B[], int n) {
        if ((NULL == A) || (m == 0))
        {
            // copy B to A directly
            for(int ii = 0; ii < n; ++ii)
            {
                A[ii] = B[ii];
            }
            return;
        }
        if ((NULL == B) || (n == 0))
        {
            // A remains as it is
            return;
        }
        int ii;
        int jj_a = m-1;
        int kk_b = n-1;
        for(ii =  m+n-1; ii >= 0; --ii)
        {
            /*if (A[jj_a] <= B[kk_b])
            {
                A[ii] = B[kk_b--];
            }else
            {
                A[ii] = A[jj_a--];
            }*/
            A[ii] = A[jj_a] <= B[kk_b] ? B[kk_b--] : A[jj_a--];
            // at least one arrary has been checked completely
            if ((kk_b < 0) | ( jj_a < 0))
            {
                ii--;
                break;
            }
        }
        
        // if B has elements remaining unchecked, copy them
        // if A has elements remaining unckecked, just keep them
        if ( (jj_a < 0) & (kk_b >= 0))
        {
            for (; ii >= 0; --ii)
            {
                A[ii] = B[kk_b--];
            }
        }
        
    }
};