merge_sorted_array.cpp

/*
Problem Statement :- You are given two integer arrays nums1 and nums2, sorted in non-decreasing order,
and two integers m and n, representing the number of elements in nums1 and nums2 respectively.
Merge nums1 and nums2 into a single array sorted in non-decreasing order.
The final sorted array should not be returned by the function, but instead be stored inside the array nums1. 
To accommodate this, nums1 has a length of m + n, where the first m elements denote the elements that should be merged, 
and the last n elements are set to 0 and should be ignored. nums2 has a length of n.
Example 1 :-
Input: nums1 = [1,2,3,0,0,0], m = 3, nums2 = [2,5,6], n = 3
Output: [1,2,2,3,5,6]
Explanation: The arrays we are merging are [1,2,3] and [2,5,6].
The result of the merge is [1,2,2,3,5,6] with the underlined elements coming from nums1.
Example 2 :-
Input: nums1 = [1], m = 1, nums2 = [], n = 0
Output: [1]
Explanation: The arrays we are merging are [1] and [].
The result of the merge is [1].
Example 3 :-
Input: nums1 = [0], m = 0, nums2 = [1], n = 1
Output: [1]
Explanation: The arrays we are merging are [] and [1].
The result of the merge is [1].
Note that because m = 0, there are no elements in nums1. The 0 is only there to ensure the merge result can fit in nums1.
*/
// Two Pointer Approch From index 0;

void merge( vector < int > & nums1 , int m , vector< int > & nums2 , int n ) {
        int i , j = 0 , u = 0 ;
        vector< int > temp ;
        
        for( i = 0 ; i < m ; i++ )
            temp.push_back( nums1[i] ) ;       // Copying the element form num1 that is needed to merged
            
        i = 0 ;
        while( i < m && j < n ){
        
            if( temp[i] > nums2[j] ) 
                nums1[ u++ ] = nums2[ j++ ] ;
            else
                nums1[ u++ ] = temp[ i++ ] ;
        }
        
         while( i < m )
            nums1[ u++ ] = temp[ i++ ] ;
            
         while( j < n )
            nums1[ u++ ] = nums2[ j++ ] ;
            
}

// Two Pointer Approch From index last

 void merge( vector< int > & nums1 , int m , vector< int > & nums2 , int n ) {
       
        int  j = n-1 , i = m-1 , k = m+n-1 ;
        
        while( j >= 0 ){
            if( i >= 0 && nums1[ i ] > nums2[ j ] ) 
                nums1[ k-- ] = nums1[ i-- ] ;
            else
                nums1[ k-- ] = nums2[ j-- ] ;
                
        }
    }
/*
Tip :- Dry Run this code on Copy to Understand the key factors.
*/