Array2

Problem1.java

@@ -0,0 +1,20 @@
+class Problem1 {
+    public List<Integer> findDisappearedNumbers(int[] nums) {
+
+        List<Integer> result = new ArrayList<>();
+        HashSet<Integer> set = new HashSet<>();
+        int n = nums.length;
+
+        for(int i=0; i<n; i++){
+            set.add(nums[i]);
+        }
+
+        for(int i=1; i<=n; i++){
+            if(!set.contains(i)){
+                result.add(i);
+            }
+        }
+
+        return result;
+    }
+}

Problem2.java

@@ -0,0 +1,48 @@
+class Problem2 {
+    int[][] dirs;
+    int m,n;
+
+    public void gameOfLife(int[][] board) {
+
+        this.dirs = new int[][]{{-1,-1}, {-1,0}, {-1, 1}, {0, -1}, {0, 1}, {1,-1}, {1,0}, {1,1}};
+
+        this.m = board.length;
+        this.n = board[0].length;
+
+        for(int i=0; i<m; i++){
+            for(int j=0; j<n; j++){
+                int count = getCount(board, i, j);  // number of alive cells around it
+                if(board[i][j] == 0 && count == 3){
+                    board[i][j] = 3; // dead -> alive;
+                }else if(board[i][j] == 1 && (count < 2 || count >3)){
+                    board[i][j] = 2; // alive -> dead;
+                }
+            }
+        }
+
+        for(int i=0; i<m; i++){
+            for(int j=0; j<n; j++){
+                if(board[i][j] == 2){
+                    board[i][j] = 0;
+                }else if(board[i][j] == 3){
+                    board[i][j] = 1;
+                }
+            }
+        }
+    }
+
+    private int getCount(int[][] board, int i, int j){
+        int count = 0;
+
+        for(int[] dir: dirs){
+            int r = i + dir[0];
+            int c = j + dir[1];
+
+            if(r>=0 && c>=0 && r<m && c<n){ 
+                if(board[r][c] == 1 || board[r][c] == 2) count++;
+            }
+        }
+
+        return count;
+    }
+}