LintCode Merge Sorted Array II

Merge two given sorted integer array A and B into a new sorted integer array.

Example

A=[1,2,3,4]

B=[2,4,5,6]

return [1,2,2,3,4,4,5,6]

Challenge

How can you optimize your algorithm if one array is very large and the other is very small?

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解题思路：

从后往前填空，从最大的往最小的填写。O(m+n)

Challenge 答案：

效率上优化。假如A很小，B很大，那么合并就可以将A中的值插入到B中，B可以整体copy到新array里，整体拷贝的效率大于一个一个拷贝的速度快。

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Java code:

class Solution {
    /**
     * @param A and B: sorted integer array A and B.
     * @return: A new sorted integer array
     */
    public int[] mergeSortedArray(int[] A, int[] B) {
        // Write your code here
        int i = A.length - 1, j = B.length - 1;
        int length = A.length + B.length;
        int index = length - 1;
        int[] C = new int[length];
        while(i >= 0 && j >= 0) {
            if(A[i] > B[j]) {
                C[index--] = A[i--];
            }else {
                C[index--] = B[j--];
            }
        }
        while(i >= 0) {
            C[index--] = A[i--];
        }
        while(j >= 0){
            C[index--] = B[j--];
        }
        return C;
    }
}