661 Image Smoother

class Solution {
    public int[][] imageSmoother(int[][] M) {
        int n = M.length, m = M[0].length;
        int[][] ans = new int[n][m];

        for (int i = 0; i < n; i++){
            for (int j = 0; j < m; j++){
                int count  = 0;
                for (int x = i - 1; x <= i + 1; x++){
                    for (int y = j - 1; y <= j + 1; y++){
                        if (x >= 0 && x < n && y >= 0 && y < m){
                            ans[i][j] += M[x][y];
                            count++;    
                        }
                    }
                }
                ans[i][j] /= count;
            }
        }

        return ans;
    }
}

289 Game of Life

class Solution {

    private Set<Coord> gameOfLife(Set<Coord> live) {
        Map<Coord,Integer> neighbours = new HashMap<>();
        for (Coord cell : live) {
            for (int i = cell.i-1; i<cell.i+2; i++) {
                for (int j = cell.j-1; j<cell.j+2; j++) {
                    if (i==cell.i && j==cell.j) continue;
                    Coord c = new Coord(i,j);
                    if (neighbours.containsKey(c)) {
                        neighbours.put(c, neighbours.get(c) + 1);
                    } else {
                        neighbours.put(c, 1);
                    }
                }
            }
        }
        Set<Coord> newLive = new HashSet<>();
        for (Map.Entry<Coord,Integer> cell : neighbours.entrySet())  {
            if (cell.getValue() == 3 || cell.getValue() == 2 && live.contains(cell.getKey())) {
                newLive.add(cell.getKey());
            }
        }
        return newLive;
    }

    private static class Coord {
        int i;
        int j;
        private Coord(int i, int j) {
            this.i = i;
            this.j = j;
        }
        public boolean equals(Object o) {
            return o instanceof Coord && ((Coord)o).i == i && ((Coord)o).j == j;
        }
        public int hashCode() {
            int hashCode = 1;
            hashCode = 31 * hashCode + i;
            hashCode = 31 * hashCode + j;
            return hashCode;
        }
    }

    public void gameOfLife(int[][] board) {
        Set<Coord> live = new HashSet<>();
        int m = board.length;
        int n = board[0].length;
        for (int i = 0; i<m; i++) {
            for (int j = 0; j<n; j++) {
                if (board[i][j] == 1) {
                    live.add(new Coord(i,j));
                }
            }
        };
        live = gameOfLife(live);
        for (int i = 0; i<m; i++) {
            for (int j = 0; j<n; j++) {
                board[i][j] = live.contains(new Coord(i,j))?1:0;
            }
        };

    }
}

check follow-ups : https://leetcode.com/problems/game-of-life/description/