题目描述：
Given two sorted integer arrays nums1 and nums2, merge nums2 into nums1 as one sorted array.
Note:
You may assume that nums1 has enough space (size that is greater or equal to m + n) to hold additional elements from nums2. The number of elements initialized in nums1 and nums2 are m and n respectively.
思路：
从后往前遍历两个数组，分别比较，大的放在数组 nums1 后面，直到两个数组都遍历完毕。
注：如果从前往后遍历的话，数组合并时需要将元素后移，效率低。
代码实现：
class Solution {
public void merge(int[] nums1, int m, int[] nums2, int n) {
int index = m+n-1;
int i1 = m-1;
int i2 = n-1;
while(i1>=0&&i2>=0){
if(nums1[i1]>=nums2[i2]){
nums1[index] = nums1[i1];
i1--;
}else{
nums1[index] = nums2[i2];
i2--;
}
index--;
}
while(i1>=0){
nums1[index] = nums1[i1];
i1--;
index--;
}
while(i2>=0){
nums1[index] = nums2[i2];
i2--;
index--;
}
}
}