From a73455ec9fd47936289c73b34ce4006a916b4a50 Mon Sep 17 00:00:00 2001
From: PrakarshKamal <kamalp@mcmaster.ca>
Date: Thu, 19 Feb 2026 16:56:35 -0500
Subject: [PATCH] Complete Array-2

---
 DisappearingNumbers.java |  43 ++++++++++++
 GameOfLife.java          | 139 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 182 insertions(+)
 create mode 100644 DisappearingNumbers.java
 create mode 100644 GameOfLife.java

diff --git a/DisappearingNumbers.java b/DisappearingNumbers.java
new file mode 100644
index 00000000..907bb5a1
--- /dev/null
+++ b/DisappearingNumbers.java
@@ -0,0 +1,43 @@
+import java.util.*;
+
+// O(n) time, O(n) space
+// class Solution {
+//     public List<Integer> findDisappearedNumbers(int[] nums) {
+//         List<Integer> ans = new ArrayList<>();
+//         Set<Integer> set = new HashSet<>();
+
+//         for (int num : nums) {
+//             set.add(num);
+//         }
+
+//         for (int i = 1; i <= nums.length; i++) {
+//             if (!set.contains(i)) {
+//                 ans.add(i+1);
+//             }
+//         }
+//         return ans;
+//     }
+// }
+
+// O(n) time, O(1) space
+class Solution {
+    public List<Integer> findDisappearedNumbers(int[] nums) {
+        List<Integer> ans = new ArrayList<>();
+        int n = nums.length;
+
+        for (int i = 0; i < n; i++) {
+            int idx = Math.abs(nums[i]) - 1; // idx of number
+
+            if (nums[idx] > 0) {
+                nums[idx] = nums[idx] * -1;
+            }
+        }
+
+        for (int i = 0; i < n; i++) {
+            if (nums[i] > 0) {
+                ans.add(i+1);
+            }
+        }
+        return ans;
+    }
+}
\ No newline at end of file
diff --git a/GameOfLife.java b/GameOfLife.java
new file mode 100644
index 00000000..f4378911
--- /dev/null
+++ b/GameOfLife.java
@@ -0,0 +1,139 @@
+// O(n * m) time, O(n * m) space
+// class Solution {
+//     public void gameOfLife(int[][] board) {
+//         int n = board.length;
+//         int m = board[0].length;
+//         int[][] copy = new int[n][m];
+
+//         int[][] dirs = new int[][] {
+//             {0,1},
+//             {0,-1},
+//             {1,0},
+//             {-1,0},
+//             {1,1},
+//             {-1,1},
+//             {1,-1},
+//             {-1,-1}
+//         };
+
+//         for (int i = 0; i < n; i++) {
+//             for (int j = 0; j < m; j++) {
+//                 copy[i][j] = board[i][j];
+//             }
+//         }
+
+//         for (int i = 0; i < n; i++) {
+//             for (int j = 0; j < m; j++) {
+//                 int cell = board[i][j];
+//                 int live = getLiveNeighbors(i, j, board, dirs);
+
+//                 if (cell == 1 && (live < 2 || live > 3)) {
+//                     copy[i][j] = 0;
+//                 }
+//                 else if (cell == 1 && (live == 2 || live == 3)) {
+//                     copy[i][j] = 1;
+//                 }
+//                 else if (cell == 0 && live == 3) {
+//                     copy[i][j] = 1;
+//                 }
+//                 else {
+//                     copy[i][j] = 0;
+//                 }
+//             }
+//         }
+
+//         for (int i = 0; i < n; i++) {
+//             for (int j = 0; j < m; j++) {
+//                 board[i][j] = copy[i][j];
+//             }
+//         }
+//     }
+
+//     private int getLiveNeighbors(int i, int j, int[][] board, int[][] dirs) {
+//         int n = board.length;
+//         int m = board[0].length;
+
+//         int liveCellCount = 0;
+
+//         for (int[] dir : dirs) {
+//             int newI = i + dir[0];
+//             int newJ = j + dir[1];
+
+//             if (newI >= 0 && newJ >= 0 && newI < n && newJ < m) {
+//                 if (board[newI][newJ] == 1) {
+//                     liveCellCount++;
+//                 }
+//             }
+//         }
+//         return liveCellCount;
+//     }
+// }
+
+// O(n * m) time, O(1) space
+class Solution {
+    public void gameOfLife(int[][] board) {
+        int n = board.length;
+        int m = board[0].length;
+
+        int[][] dirs = new int[][] {
+            {0,1},
+            {0,-1},
+            {1,0},
+            {-1,0},
+            {1,1},
+            {-1,1},
+            {1,-1},
+            {-1,-1}
+        };
+
+        for (int i = 0; i < n; i++) {
+            for (int j = 0; j < m; j++) {
+                int cell = board[i][j];
+                int live = getLiveNeighbors(i, j, board, dirs);
+
+                if (cell == 1 && (live < 2 || live > 3)) {
+                    board[i][j] = 5; // was alive now dead, alive -> dead
+                }
+                else if (cell == 1 && (live == 2 || live == 3)) {
+                    board[i][j] = 1;
+                }
+                else if (cell == 0 && live == 3) {
+                    board[i][j] = 10; // was dead now alive, dead -> alive
+                }
+                else {
+                    board[i][j] = 0;
+                }
+            }
+        }
+
+        for (int i = 0; i < n; i++) {
+            for (int j = 0; j < m; j++) {
+                if (board[i][j] == 5) { // alive -> dead so now mark dead
+                    board[i][j] = 0;
+                }
+                else if (board[i][j] == 10) { // dead -> alive so now mark alive
+                    board[i][j] = 1;
+                }
+            }
+        }
+    }
+
+    private int getLiveNeighbors(int i, int j, int[][] board, int[][] dirs) {
+        int n = board.length;
+        int m = board[0].length;
+
+        int liveCellCount = 0;
+
+        for (int[] dir : dirs) {
+            int newI = i + dir[0];
+            int newJ = j + dir[1];
+
+            if (newI >= 0 && newJ >= 0 && newI < n && newJ < m) {
+                if (board[newI][newJ] == 1 || board[newI][newJ] == 5) {
+                    liveCellCount++;
+                }
+            }
+        }
+        return liveCellCount;
+    }
+}
\ No newline at end of file