496. Next Greater Element I

/*Runtime: 4 ms, faster than 55.52% of Java online submissions for Next Greater Element I.
Memory Usage: 38.9 MB, less than 86.14% of Java online submissions for Next Greater Element I.
*/

class Solution {
    public int[] nextGreaterElement(int[] nums1, int[] nums2) {
        
       HashMap<Integer, Integer> next_greatest = new HashMap();
        Stack<Integer> stack = new Stack() ;
        
        for (Integer num : nums2)
        {
            while(!stack.isEmpty() && stack.peek() < num)
            {
                next_greatest.put(stack.pop(), num);
            }
            stack.push(num) ; 
        }
         for(int i=0;i<nums1.length;i++)
         {
             nums1[i]=next_greatest.getOrDefault(nums1[i],-1);
         }
        
        return nums1;
    }
}




/*

Runtime: 18 ms, faster than 5.82% of Java online submissions for Next Greater Element I.
Memory Usage: 38.7 MB, less than 97.31% of Java online submissions for Next Greater Element I.

ArrayList<Integer> arr=new ArrayList<>();
        
        for(int i:nums2)
            arr.add(i);
        
        
        
        int[] result=new int[nums1.length];
        
        for(int i=0;i<nums1.length;i++)
        {   int greatest=nums1[i];
            int index=arr.indexOf(nums1[i]);
                
                for(int j=index;j<arr.size();j++)
                {
                    if(arr.get(j)>greatest){
                        greatest=arr.get(j);
                        result[i]=arr.get(j);
                    }
                    if(greatest!=nums1[i])
                        break;
                }
            
            if(greatest==nums1[i])
                result[i]=-1;
         
        }
        
        return result;

*/