JAVA - How to find duplicate values in rows and columns in a 2D Array?

I have a 2D Array and I would like to find an easier way to manipulate my code so that it will find if there is a duplicate in the column and easier way then what I have below:

for (int i=0; i < array.length; i++) {
    for (int j=0; j < array.length; j++) {
        for (int k=1; k < array.length; k++){
            if (array[j+k][i] == array[j][i]) {
               if (array[j][i] != 0) {
                return true;
               }
            }
        }
    } 
  }  
return false;

E开发者_开发百科DIT: KINDLY POINTED OUT THE ABOVE ^^ WON'T WORK EITHER AS IT WILL THROW AN OUT OF BOUNDS EXCEPTION

This way has too many loops and I am sure there must be an easier way to find duplicates rather than going through this massive looping process.

This is for a square 2D array, ie. an array with rows = columns.

If so, how can this new way work - and how can I manipulate it to work to find duplicate values in the rows as well.

Thanks for the help.

you can use HashSet to store all already encountered elements. should be something like this:

static boolean noDupes(int[][] array) {
    for (int i=0; i < array.length; i++) {
        HashSet<Integer> set = new HashSet<Integer>();
        for (int j=0; j < array.length; j++) {
            if (set.contains(array[j][i])) return false;
            set.add(array[j][i]);
        }
    }
    return true;
}

this solution is O(length^2) = O(n) where n is the matrix total size. I think it is ideal in terms of big O, because you need to check all elements.

int[][] array = new int[3][5];

for (int i = 0; i < array.length; i++) // array initialization
  for (int j = 0; j < array[i].length; j++ )
    array[i][j] = i*j;

Map<Integer, Set<Point>> map = new HashMap<Integer, Set<Point>>();

for (int i = 0; i < array.length; i++)
  for (int j = 0; j < array[i].length; j++)
    if (map.containsKey(array[i][j]))
      map.get(array[i][j]).add(new Point(i, j));
    else
    {
      Set<Point> set = new HashSet<Point>();
      set.add(new Point(i, j));
      map.put(array[i][j], set);
    }


for (Map.Entry<Integer, Set<Point>> entry : map.entrySet())
  if (entry.getValue().size() > 1)
  {
    System.out.println("value = " + entry.getKey());
    for (Point p : entry.getValue())
      System.out.println("coordinates = " + p);
    System.out.println();
  }

The output is as expected:

value = 0
coordinates = java.awt.Point[x=0,y=3]
coordinates = java.awt.Point[x=0,y=0]
coordinates = java.awt.Point[x=2,y=0]
coordinates = java.awt.Point[x=0,y=4]
coordinates = java.awt.Point[x=0,y=2]
coordinates = java.awt.Point[x=1,y=0]
coordinates = java.awt.Point[x=0,y=1]

value = 2
coordinates = java.awt.Point[x=1,y=2]
coordinates = java.awt.Point[x=2,y=1]

value = 4
coordinates = java.awt.Point[x=2,y=2]
coordinates = java.awt.Point[x=1,y=4]

Finding the Duplicate Elements in a given Matrix - JAVA

static void findDuplicates(String[][] matrix) {
    HashSet<String> uniqInp = new HashSet<String>();
    HashSet<String> allDup = new HashSet<String>();
    System.out.println("***** DUPLICATE ELEMENTS *****");

    for(int row=0;row<matrix.length;row++) 
    {
        for(int col=0;col<matrix[0].length;col++)
        {
            if(uniqInp.add(matrix[row][col]))
                //If not duplicate it will add
                continue;
            else {
                // If Duplicate element found, it will come here
                if(allDup.add(matrix[row][col]))
                System.out.print(matrix[row][col]+" ");
            }
        }
    }
}