public static boolean checkDuplicateWithinK(int[][] mat, int k){    class Cell{        int row;        int col;        public Cell(int r, int c){            this.row = r;            this.col = c;        }    }    int n = mat.length;    int m = mat[0].length;    k = Math.min(k, n*m);    //map from distance to cell postions of the matrix    Map
    
     > map = new HashMap
     
      >();    for(int i = 0; i < n; i++){        for(int j = 0; j < m; j++){            if(map.containsKey(mat[i][j])){                for(Cell c : map.get(mat[i][j])){                    int Dist = Math.abs(i - c.row)+Math.abs(j - c.col);                    if(Dist <= k){                        return true;                    }                    if(i - c.row > k){                        map.remove(c);                    }                }                map.get(mat[i][j]).add(new Cell(i, j));            }            else{                map.put(mat[i][j], new HashSet
      
       ());                map.get(mat[i][j]).add(new Cell(i, j));            }        }    }    return false;}
      
     
    

public boolean checkDuplicatesWithinK(int[][] matrix, int k) {        //convert matrix to an array        int[] arr = Arrays.stream(matrix)                .flatMapToInt(Arrays::stream)                .toArray();        // Creates an empty hashset        HashSet
    
      set = new HashSet<>();        // Traverse the input array        for (int i = 0; i < arr.length; i++) {            // If already present n hash, then we found            // a duplicate within k distance            if (set.contains(arr[i]))                return true;            // Add this item to hashset            set.add(arr[i]);            // Remove the k+1 distant item            if (i >= k)                set.remove(arr[i - k]);        }            return false;    }