Leetcode 88. Merge Sorted Array

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 nums1and nums2 are m and n respectively.

解题思路：

The key to solve this problem is moving element of A and B backwards. If B has some elements left after A is done, also need to handle that case.

从后往前填空。九章算法也是这么讲的。

Java code:

public void merge(int[] nums1, int m, int[] nums2, int n) {
        //from back to front
        int k = m+n-1;
        int i = m-1;
        int j = n-1;
        for(; i >= 0 && j >= 0; k--) {
            if(nums1[i] >= nums2[j]) {
                nums1[k] = nums1[i--];
            }else{
                nums1[k] = nums2[j--];
            }
        }
        while(j >= 0) {
            nums1[k--] = nums2[j--];
        }
    }

2. 九章算法答案 2016.01.18

public class Solution {
    public void merge(int[] nums1, int m, int[] nums2, int n) {
        int i = m-1, j = n-1, index = m + n - 1;
        while( i >= 0 && j >= 0) {
            if(nums1[i] > nums2[j]) {
                nums1[index--] = nums1[i--];
            }else {
                nums1[index--] = nums2[j--];
            }
        }
        while( j >= 0) {
            nums1[index--] = nums2[j--];
        }
    }
}

Reference:

1. http://www.programcreek.com/2012/12/leetcode-merge-sorted-array-java/

2. http://fisherlei.blogspot.com/2012/12/leetcode-merge-sorted-array.html