leetcode — merge-sorted-array

import java.util.Arrays;

/**
* Source : https://oj.leetcode.com/problems/merge-sorted-array/ *
*
* 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.
*/
public class MergeSortedArray {

/**
* 将数组B合并到数组A，数组A空间足够大能放得下B
* 合并两个排序的数组，使用两个指针分别指向两个数组，然后比较大小将较小的放到数组A中，
*          如果把小的放在前面可能回把A中的元素覆盖（数组排序是升序的）
*
* 所以可以考虑从两个数组的末尾开始合并，将较大的元素放在A数组的最后
*
* 如果任意一个数组遍历完了，把B中剩下的元素依次插入A中
* @param a
* @param b
* @return
*/
public int[] merge (int[] a, int m, int[] b, int n) {
int pa = m - 1;
int pb = n - 1;
int pc = m + n - 1;
while (pa > -1 && pb > -1) {
if (a[pa] > b[pb]) {
a[pc--] = a[pa--];
} else {
a[pc--] = b[pb--];
}
}
while (pb > -1) {
a[pc--] = b[pb--];
}
return a;
}

public static void main(String[] args) {
MergeSortedArray mergeSortedArray = new MergeSortedArray();
int[] a = new int[]{1,5,9,0,0,0,0};
int[] b = new int[]{2,3,8};

System.out.println(Arrays.toString(mergeSortedArray.merge(a, 3, b, 3)));
}
}