lintcode:Merge Sorted Array

最新推荐文章于 2019-10-25 10:26:54 发布

原创最新推荐文章于 2019-10-25 10:26:54 发布 · 507 阅读

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本文介绍了一种高效的方法将两个已排序的整数数组A和B合并成一个有序数组A。通过避免使用额外的数组空间，直接在A数组中进行操作，从而实现了空间效率和时间效率的双重提升。

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

Example
A = [1, 2, 3, empty, empty], B = [4, 5]

After merge, A will be filled as [1, 2, 3, 4, 5]

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.

1.提交1

class Solution {
public:
    /**
     * @param A: sorted integer array A which has m elements, 
     *           but size of A is m+n
     * @param B: sorted integer array B which has n elements
     * @return: void
     */
    void mergeSortedArray(int A[], int m, int B[], int n) {
        // write your code here
        int *res=new int[m+n];
        for(int i=0;i<m;i++){
            res[i]=A[i];
        }

        for(int i=m;i<m+n;i++){
            res[i]=B[i-m];
        }

        sort(res,res+m+n);//

        memcpy(A,res,sizeof(int)*(m+n));
        delete []res;
    }
};

虽然AC，但很明显未充分利用有序的特点

2.提交2

class Solution {
public:
    /**
     * @param A: sorted integer array A which has m elements, 
     *           but size of A is m+n
     * @param B: sorted integer array B which has n elements
     * @return: void
     */
    void mergeSortedArray(int A[], int m, int B[], int n) {
        // write your code here
        //上个实现明显不好
        //其实这个就是归并排序的归并阶段
        int pa=m-1,pb=n-1,p=m+n-1;
        while(pa>=0&&pb>=0){
            if(A[pa]>=B[pb]){
                A[p]=A[pa];
                p--;
                pa--;
            }else{
                A[p]=B[pb];
                p--;
                pb--;
            }
        }

        while(pa>=0){
            A[p--]=A[pa--];
        }
        while(pb>=0){
            A[p--]=B[pb--];
        }
    }
};