_88.java

package com.fishercoder.solutions;

/**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.*/

public class _88 {

    //credit:https://discuss.leetcode.com/topic/2461/this-is-my-ac-code-may-help-you
    public static void merge_O1_space(int[] nums1, int m, int[] nums2, int n) {
        int i = m-1;
        int j = n-1;
        int k = m+n-1;
        while (i >= 0 && j >= 0) {
            if (nums1[i] > nums2[j]) nums1[k--] = nums1[i--];
            else nums1[k--] = nums2[j--];
        }
        while (j >= 0) nums1[k--] = nums2[j--];
    }

    /**I used O(m) extra space to create a temp array, but this could be optimized.*/
    public static void merge(int[] nums1, int m, int[] nums2, int n) {
        int[] temp = new int[m];
        for(int i = 0; i < m; i++) temp[i] = nums1[i];
        for(int i = 0, j = 0, k = 0; i < m || j < n;){
            if(i == m){
                for(; j < n;){
                    nums1[k++] = nums2[j++];
                }
                break;
            }
            if(j == n){
                for(; i < m;){
                    nums1[k++] = temp[i++];
                }
                break;
            }
            
            if(temp[i] > nums2[j]){
                nums1[k++] = nums2[j++];
            } else {
                nums1[k++] = temp[i++];
            }
        }
    }

    public static void main(String...args){
//        int[] nums1 = new int[]{2,0};
//        int m = 1;
//        int[] nums2 = new int[]{1};
//        int n = 1;
        
        int[] nums1 = new int[]{4,5,6,0,0,0};
        int m = 3;
        int[] nums2 = new int[]{1,2,3};
        int n = 3;
        merge(nums1, m, nums2, n);
    }
}