88. Merge Sorted Array (https://leetcode.com/problems/merge-sorted-array/): Given two sorted integer arrays nums1 and nums2, merge nums2 into nums1 as one sorted array. Note: The number of elements initialized in nums1 and nums2 are m and n respectively. You may assume that nums1 has enough space (size that is greater or equal to m + n) to hold …

88. Merge Sorted Array (#1 Two pointer).java

// Two pointer solution: read/write (end/end) pointer
// Time: O(m + n), 0ms
// Space: O(1), 36.3mb
class Solution {
    public void merge(int[] nums1, int m, int[] nums2, int n) {
        // Two read pointers for nums1 and nums2, and 1 write pointer for nums1
        int r1 = m - 1, r2 = n - 1, w = m + n - 1;
        
        while(w >= 0) {
            // **: Merge two into one: handle the cases when one of them is out of elements 658 #1.1
            if(r2 < 0 || r1 >= 0 && nums1[r1] >= nums2[r2]) {
                nums1[w--] = nums1[r1--];
            } else {
                nums1[w--] = nums2[r2--];
            }
        }
    }
}
// end/end pointers
//********
//<=^  <=^
//  i
//*****
//  <=^
//    j