Initialize game board in matrix

Initialize game board in matrix is to populate one digit number into a MxN matrix. The digit can be generated randomly. However, no 3 adjacent cells shall be the same, horizontal, vertical, diagonal and L shape. If you find invalid digit, replace with a different one in that cell.

Matrix is 2D array, which reflects the game in real world. The popular game board questions such as tic tac toe, sudoku, or chess board, all use matrix. Note the cells at the edge has no adjacent cells. So the index should be offset 1 from the edge.

Question:
Initialize a M X N board with integer 0, 10, in which no 3 adjacent cells are the same.
The 3 adjacent cells are might be in horizontal line, vertical line, diagonal line, or L shapes.

Java

import java.util.ArrayList;
import java.util.List;
 
public class InitializeGameBoard {
	public static int randomInt(int m) {
        return (int) (Math.random() * m);
    }
	
	public static int[][] initialize(int n, int m) {
	    int[][] result = new int[n][n];	   
	    for (int i = 0; i < n; i++)
	    	for (int j = 0; j < n;j++)
	    		result[i][j] = randomInt (m);
	    return result;
	}
	
	public static int randomNotIn(int m, int n ) {  // K is sorted
		List<Integer> uSet = new ArrayList<Integer>();
		for (int i = 0; i < m;i++) {
			uSet.add(i);
		}
		
		uSet.remove(uSet.indexOf(n));
		
		int un = randomInt(uSet.size());
		return uSet.get(un);
	}
	
	static void validateBoard (int[][] a, int m) {
	
		for (int i =1;i<a.length-1; i++)
			for (int j=1; j<a.length-1; j++) {
				//left and right
				if (a[i][j] == a[i][j-1] && a[i][j] == a[i][j+1]) {
					System.out.println("found horizontal conjuction:"+a[i][j]);
					a[i][j] = randomNotIn (m, a[i][j]);
				}
				//upper and below
				if (a[i][j] == a[i-1][j] && a[i][j] == a[i+1][j] ) {
					System.out.println("found vertical conjuction:"+a[i][j]);
					a[i][j] = randomNotIn (m, a[i][j]);
				}
				//Diagonal  
				if (a[i][j] == a[i-1][j-1] && a[i][j] == a[i+1][j+1] ){
					System.out.println("found left diagonal conjuction:"+a[i][j]);
					a[i][j] = randomNotIn (m, a[i][j]);
				}
				//Diagonal  
				if (a[i][j] == a[i-1][j+1] && a[i][j] == a[i+1][j-1] ){
					System.out.println("found right diagonal conjuction:"+ a[i][j]);
					a[i][j] = randomNotIn (m, a[i][j]);
				}
				// left and upper
				if (a[i][j] == a[i][j-1] && a[i][j] == a[i-1][j] ){
					System.out.println("found L sharps face left conjuction:" + a[i][j]);
					a[i][j] = randomNotIn (m, a[i][j]);
				}
				//right and upper
				if (a[i][j] == a[i][j+1] && a[i][j] == a[i-1][j] ) {
					System.out.println("found L sharps conjuction:"+ a[i][j]);
					a[i][j] = randomNotIn (m, a[i][j]);
				}
				//left and lower
				if (a[i][j] == a[i][j-1] && a[i][j] == a[i+1][j] ){
					System.out.println("found L sharps face left down conjuction:"+ a[i][j]);
					a[i][j] = randomNotIn (m, a[i][j]);
				}
				//right and lower
				if (a[i][j] == a[i][j+1] && a[i][j] == a[i+1][j] ){
					System.out.println("found L sharps face down conjuction:"+ a[i][j]);
					a[i][j] = randomNotIn (m, a[i][j]);
				}							
			}
					
	}
	
	private static void showBoard(int[][] a) {		  
	    for (int i = 0; i < a.length; i++) {
	    	for (int j = 0;j <a.length; j++)
	    		System.out.print(a[i][j]+" ");
	    	System.out.println();
	    }
	}
	public static void main(String[] args) {
		int size = 8;
		int range = 10; 
		int[][] result = initialize(size, range);
		showBoard(result);
		System.out.println();
      
		validateBoard (result, range);
		System.out.println();
		showBoard(result);
	}
}
}

import java.util.ArrayList;

import java.util.List;

public class InitializeGameBoard {

public static int randomInt(int m) {

return (int) (Math.random() * m);

}

public static int[][] initialize(int n, int m) {

int[][] result = new int[n][n];

for (int i = 0; i < n; i++)

for (int j = 0; j < n;j++)

result[i][j] = randomInt (m);

return result;

}

public static int randomNotIn(int m, int n ) { // K is sorted

List<Integer> uSet = new ArrayList<Integer>();

for (int i = 0; i < m;i++) {

uSet.add(i);

}

uSet.remove(uSet.indexOf(n));

int un = randomInt(uSet.size());

return uSet.get(un);

}

static void validateBoard (int[][] a, int m) {

for (int i =1;i<a.length-1; i++)

for (int j=1; j<a.length-1; j++) {

//left and right

if (a[i][j] == a[i][j-1] && a[i][j] == a[i][j+1]) {

System.out.println("found horizontal conjuction:"+a[i][j]);