import java.util.*;
public class AStar {
public static
final int DIAGONAL_COST = 14;
public static
final int V_H_COST = 10;
static class
Cell{
int
heuristicCost = 0; //Heuristic cost
int finalCost =
0; //G+H
int i, j;
Cell parent;
Cell(int i, int
j){
this.i = i;
this.j = j;
}
@Override
public String
toString(){
return
"["+this.i+", "+this.j+"]";
}
}
//Blocked cells are
just null Cell values in grid
static Cell [][]
grid = new Cell[5][5];
static
PriorityQueue<Cell> open;
static boolean
closed[][];
static int
startI, startJ;
static int endI,
endJ;
public static
void setBlocked(int i, int j){
grid[i][j] =
null;
}
public static
void setStartCell(int i, int j){
startI = i;
startJ = j;
}
public static
void setEndCell(int i, int j){
endI = i;
endJ = j;
}
static
void checkAndUpdateCost(Cell current, Cell t, int cost){ if(t == null ||
closed[t.i][t.j])return;
int t_final_cost
= t.heuristicCost+cost;
boolean inOpen =
open.contains(t);
if(!inOpen ||
t_final_cost<t.finalCost){
t.finalCost =
t_final_cost;
t.parent =
current;
if(!inOpen)open.add(t);
}
}
public static
void AStar(){
//add the start
location to open list.
open.add(grid[startI][startJ]);
Cell current;
while(true){
current =
open.poll();
if(current==null)break;
closed[current.i][current.j]=true;
if(current.equals(grid[endI][endJ])){
return;
}
Cell t;
if(current.i-1>=0){
t = grid[current.i-1][current.j];
checkAndUpdateCost(current,
t, current.finalCost+V_H_COST); if(current.j-1>=0){
t =
grid[current.i-1][current.j-1];
checkAndUpdateCost(current,
t, current.finalCost+DIAGONAL_COST);
}
if(current.j+1<grid[0].length){
t = grid[current.i-1][current.j+1];
checkAndUpdateCost(current,
t, current.finalCost+DIAGONAL_COST);
}
}
if(current.j-1>=0){
t =
grid[current.i][current.j-1];
checkAndUpdateCost(current,
t, current.finalCost+V_H_COST);
}
if(current.j+1<grid[0].length){
t =
grid[current.i][current.j+1];
checkAndUpdateCost(current,
t, current.finalCost+V_H_COST);
}
if(current.i+1<grid.length){
t =
grid[current.i+1][current.j];
checkAndUpdateCost(current,
t, current.finalCost+V_H_COST);
if(current.j-1>=0){
t = grid[current.i+1][current.j-1];
checkAndUpdateCost(current,
t, current.finalCost+DIAGONAL_COST);
}
if(current.j+1<grid[0].length){
t =
grid[current.i+1][current.j+1];
checkAndUpdateCost(current,
t, current.finalCost+DIAGONAL_COST);
}
}
}
}
/* Params : tCase =
test case No.
x, y = Board's
dimensions
si, sj = start
location's x and y coordinates
ei, ej = end
location's x and y coordinates
int[][] blocked
= array containing inaccessible cell coordinates */
public
static void test(int tCase, int x, int y, int si, int sj, int ei, int ej,
int[][] blocked){ System.out.println("\n\nTest Case #"+tCase);
//Reset
grid = new
Cell[x][y];
closed = new
boolean[x][y];
open
= new PriorityQueue<>((Object o1, Object o2) -> { Cell c1 = (Cell)o1;
Cell c2 = (Cell)o2;
return
c1.finalCost<c2.finalCost?-1: c1.finalCost>c2.finalCost?1:0;
});
//Set start
position
setStartCell(si,
sj); //Setting to 0,0 by default. Will be useful for the UI part
//Set End
Location
setEndCell(ei,
ej);
for(int
i=0;i<x;++i){
for(int
j=0;j<y;++j){
grid[i][j] = new
Cell(i, j);
grid[i][j].heuristicCost
= Math.abs(i-endI)+Math.abs(j-endJ);
}
}
grid[si][sj].finalCost
= 0;
/*Set
blocked cells. Simply set the cell values to null for blocked cells*/ for(int
i=0;i<blocked.length;++i){
setBlocked(blocked[i][0],
blocked[i][1]);
}
//Display
initial map
System.out.println("Grid:
");
for(int
i=0;i<x;++i){
for(int
j=0;j<y;++j){
if(i==si&&j==sj)System.out.print("SO
"); //Source
else
if(i==ei && j==ej)System.out.print("DE "); //Destination else
if(grid[i][j]!=null)System.out.printf("%-3d ", 0); else
System.out.print("BL ");
}
System.out.println();
}
System.out.println();
AStar();
System.out.println("\nScores
for cells: ");
for(int
i=0;i<x;++i){
for(int
j=0;j<x;++j){
if(grid[i][j]!=null)System.out.printf("%-3d
", grid[i][j].finalCost);
else
System.out.print("BL ");
}
System.out.println();
}
System.out.println();
if(closed[endI][endJ]){
System.out.println("Path:
");
Cell current =
grid[endI][endJ];
System.out.print(current);
while(current.parent!=null){
System.out.print("
-> "+current.parent);
current =
current.parent;
}
System.out.println();
}else
System.out.println("No possible path");
}
public static
void main(String[] args) throws Exception{
//test
case , grid size, start and end position and array of blocked links test(1, 5,
5, 0, 0, 3, 2, new int[][]{{0,4},{2,2},{3,1},{3,3}});
test(2,
5, 5, 0, 0, 4, 4, new int[][]{{0,4},{2,2},{3,1},{3,3}}); test(3, 7, 7, 2, 1, 5,
4, new int[][]{{4,1},{4,3},{5,3},{2,3}}); test(1, 5, 5, 0, 0, 4, 4, new
int[][]{{3,4},{3,3},{4,3}});
}
