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 mand n respectively.

 解法一：

public class Solution {
    public void merge(int A[], int m, int B[], int n) {
        if(m==0){
            for(int i=0;i<n;i++){
                A[i] = B[i];
            }
            return;
        }
        if(n==0) return;
        int[] C = new int[m+n];//new一个大小为m+n的数组
        int a = 0,b = 0,c = 0;//三个下标
        while(a<m&&b<n){
            if(A[a]<B[b]){
                C[c++] = A[a];
                if(a==m-1){
                    while(b<n){
                        C[c++] = B[b++];//A数组遍历结束，将B数组剩下元素顺序复制到C数组
                    }
                    break;
                }
                else{
                    a++;
                }
            }
            else{
                C[c++] = B[b];
                if(b==n-1){
                    while(a<m){
                        C[c++] = A[a++];//B数组遍历结束，将A数组剩下元素顺序复制到C数组
                    }
                    break;
                }
                else{
                    b++;
                }
            }
        }
        int k = 0;
        while(k<m+n){
            A[k] = C[k];
            k++;
        }
    }
}

解法二：从后往前考虑，将2个数组中较大的存放在m+n-i位置处，i初始为1；这样每个元素存放的位置就是其最终位置，代码如下：

public class Solution {
    public void merge(int A[], int m, int B[], int n) {
       int i = m+n-1;
       int a = m-1;
       int b = n-1;
       while(a>=0&&b>=0) {
           if(A[a]>B[b]) A[i--] = A[a--];
           else A[i--] = B[b--];
       }
       while(b>=0){
           A[i--] = B[b--];
       }
    }
}