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class DSU {
    int parent[];
    int height[];
 
    public DSU(int n) {
        parent = new int[n];
        height = new int[n];
        Arrays.fill(parent , -1);
        Arrays.fill(height , 1);
    }
 
    public int findRoot(int node) {
        if(parent[node] == -1) 
            return node;
        return parent[node] = findRoot(parent[node]);
    }
 
    public boolean union(int node1 , int node2) {
        int ra = findRoot(node1);
        int rb = findRoot(node2);
        if(ra != rb) {
            if(height[ra] < height[rb])
                parent[ra] = rb;
            else if(height[ra] > height[rb])
                parent[rb] = ra;
            else {
                parent[ra] = rb;
                height[rb] ++;
            }
            return true;
        }
        return false;
    }
}
 
class Solution {
    public int swimInWater(int[][] grid) {
        int n = grid.length;
        DSU dsu = new DSU(n * n);
        List<Integer> positions = new ArrayList<>();
        for(int i = 0 ; i < n ; i ++)
            for(int j = 0 ; j < n ; j ++)
                positions.add(i * n + j);
        Collections.sort(positions , (a , b) -> grid[a / n][a % n] - grid[b / n][b % n]);
        int dir[][] = new int[][]{{0 , 1} , {0 , -1} , {-1 , 0} , {1 , 0}};
 
        for(int position : positions)
        {
            int r = position / n;
            int c = position % n;
 
            for(int i = 0 ; i < dir.length ; i ++)
            {
                int nr = r + dir[i][0];
                int nc = c + dir[i][1];
 
                if(nr >= 0 && nc >= 0 && nr < n && nc < n && grid[nr][nc] < grid[r][c])
                    dsu.union(position , nr * n + nc);
            }
 
            if(dsu.findRoot(0) == dsu.findRoot((n * n) - 1))
                return grid[r][c];
        }
 
        return -1;
    }
}

Main.java:8: error: cannot find symbol
        Arrays.fill(parent , -1);
        ^
  symbol:   variable Arrays
  location: class DSU
Main.java:9: error: cannot find symbol
        Arrays.fill(height , 1);
        ^
  symbol:   variable Arrays
  location: class DSU
Main.java:40: error: cannot find symbol
        List<Integer> positions = new ArrayList<>();
        ^
  symbol:   class List
  location: class Solution
Main.java:40: error: cannot find symbol
        List<Integer> positions = new ArrayList<>();
                                      ^
  symbol:   class ArrayList
  location: class Solution
Main.java:44: error: cannot find symbol
        Collections.sort(positions , (a , b) -> grid[a / n][a % n] - grid[b / n][b % n]);
        ^
  symbol:   variable Collections
  location: class Solution
5 errors

Standard output is empty