Finding duplicate INT in 2D array

问题

I'm stuck on this method.

public class Duplicate{


   public static boolean extra(int [][] grid)
   {
       for(int i = 0; i < grid.length; i++)
           for(int j = 0; j < grid[i].length-1; j++)
              if(grid[i][j] == grid[i][j+1])
              {
                  System.out.println(grid[i][j]);
                  return true;
              }
    return false;
   }

   public static void main(String[] args){

      int [][] grades = {{3,5,8,7},
                        {2,1,11,4},
                       {13,20,10,6},
                        {7,0,12,15}
                       };

       System.out.print(extra(grades));   
   }
 }

I want to find if there are any duplicated ints in the array. return true if there is and the int that is duplicated. My method keeps coming out FALSE. what am I doing wrong? Any help would be appreciated. Please and thank you.

回答1:

All your method is doing is checking if two consecutive elements are equal, which does not tell you anything about duplicates that are not adjacent. One way to do this would be to have a Map<Integer, Integer> that maps the values to their frequencies:

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

for (int[] row : grid) {
    for (int a : row) {
        map.put(a, map.containsKey(a) ? map.get(a) + 1 : 1);
    }
}

You can then loop over the entries of this map to find the elements with a frequency greater than or equal to 2.

回答2:

To rewrite your method so it works:

ArrayList<Integer> comeBefore = new ArrayList<Integer>();
for(int i = 0; i < grid.length; i++) {
    for(int j = 0; j < grid[i].length; j++) {
        if(comeBefore.contains(grid[i][j])) {
            System.out.println(grid[i][j]);
            return true;
        }
        comeBefore.add(grid[i][j]);
    }
}
return false;

I don't have time to think about it right now... but maybe a set or such would be a more efficient data structure to use for this. Also this code may not be right... but it's the gist of it; it's untested.

回答3:

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

回答4:

You are only comparing adjacent numbers in your loop with this line if(grid[i][j] == grid[i][j+1])

Like arshajii mentioned using a Map will is one way to do this. If you want to keep the co-ordinates of each duplicate then you could extend arshajii's answer to have a Map of Lists like so.

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

for(int i = 0; i < grid.length; i++)
{
    for(int j = 0; j < grid[i].length; j++)
    {
        int val = grid[i][j];
        if(map.containskey(val))
             map.put(val, map.get(val).add(new Point(i,j));
        else
        {
             List<Point> li = new ArrayList<>();
             li.add(new Point(i,j));
             map.put(val, li);
        }
    }
}

Then to get duplicates you find any key that has a size > 1 and you can get the co-ordinates

for(Integer key : map.ketSet())
{
     List<Point> li = map.get(key);
     if(li.size() > 1)
     {
          System.out.println("The value " + key +" was duplicated at the indices: ");
          for(Point p : li)
             System.out.println(p.x + ", " + p.y);
     }
}

But this is probably over the top!

来源：https://stackoverflow.com/questions/19286028/finding-duplicate-int-in-2d-array

标签

java

arrays

duplicates