Self-Avoiding Random Walks

/**********************************************************************************
  * Compilation: javac SelfAvoidingWalk
  * Execution: java SelfAvoidingWalk N T
  *
  * Generate T self-avoiding walks of length N.
  * Report the fraction of time the random walk is not self-intersecting.
  *
  * Simple execution: % java SelfAvoidingWalk 20 100
  * 26% deak ends
  *
  * *********************************************************************************/

public class SelfAvoidingWalk {
    public static void main(String[] args) {
        int N = Integer.parseInt(args[0]); // lattice size
        int T = Integer.parseInt(args[1]); // number of trials
        int deadEnds = 0; // trials resulting in a dead end

        for (int t = 0; t < T; t++) {
            int x = N/2, y = N/2;  // current position
            boolean[][] a = new boolean[N][N]; // intersections visited
            while (x > 0 && x < N-1 && y > 0 && y < N-1) { // check for dead end and make a random move.
                a[x][y] = true;
                if (a[x-1][y] && a[x+1][y] && a[x][y-1] && a[x][y+1]) {
                    deadEnds++;
                    break;
                }
                double r = Math.random();
                if (r < 0.25 && !a[x+1][y]) x++; // move right
                else if( r < 0.50 && !a[x-1][y]) x--; // move left
                else if (r < 0.75 && !a[x][y+1]) y++; // move up
                else if (r < 1.00 && !a[x][y-1]) y--; // move down
            }
        }
        System.out.println(100*deadEnds/T + " % dead ends");
    }
}