Completed Array-2

FindAllNumbersDisappearedinanArray.java

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+// Time Complexity : O(n)
+// Space Complexity : O(1)
+// Did this code successfully run on Leetcode : yes
+// Any problem you faced while coding this :no
+
+// Your code here along with comments explaining your approach
+/*
+This problem can also be solved by maintaining a boolean array and marking that nums[i] - 1 as true and
+return all those elements which remain false by traversing the boolean array again. But, the space complexity
+will be O(n) for boolean array.So, to optimize, we traverse through input array and make the nums[i] - 1
+index's value as negative(if not). Finally, we return all those values which remain positive(means their
+index not being called as that value is not present). We need to make sure of taking absolute value while
+computing index as there is a chance of revisiting the indices during traversal.
+ */
+class Solution {
+    public List<Integer> findDisappearedNumbers(int[] nums) {
+        List<Integer> disappearedList = new ArrayList<>();
+        int len = nums.length;
+        for(int i = 0 ; i < len ; i++) {
+            int index = Math.abs(nums[i]) - 1;
+            if(nums[index] > 0)
+                nums[index] *= -1;
+        }
+        for(int i = 0 ; i < len ; i++) {
+            if(nums[i] > 0)
+                disappearedList.add(i + 1);
+        }
+        return disappearedList;
+    }
+}

GameofLife.java

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+// Time Complexity : O(m * n)
+// Space Complexity : O(1)
+// Did this code successfully run on Leetcode : yes
+// Any problem you faced while coding this : no
+
+// Your code here along with comments explaining your approach
+/*
+We create a function to basically check all neighbours at 8 directions(if applicable) and apply the given
+problem's rules of live and dead cell count for each entry in the board.To make sure we are not counting
+recently alive or ignoring recently dead cells, we mark them with 2 and 3 and later revert them in-place
+to their actual states in the board.
+ */
+class Solution {
+    private int[][] dirs = new int[][]{{0, 1} , {1, 0} , {0, -1} , {-1, 0}, {-1, -1}, {-1, 1}, {1, 1}, {1, -1}};
+
+    public void gameOfLife(int[][] board) {
+        int m = board.length;
+        int n = board[0].length;
+
+        for(int i = 0 ; i < m ; i++) {
+            for(int j = 0 ; j < n ; j++) {
+                checkIfAlive(board, m , n, i , j);
+            }
+        }
+        // 1 -> 2 (previous alive, now dead)
+        // 0 -> 3 (previous dead, now alive)
+        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 void checkIfAlive(int[][] board, int m, int n, int i , int j) {
+        int countLiveCell = 0;
+        for(int[] dir : dirs) {
+            int x = i + dir[0];
+            int y = j + dir[1];
+            if(x < 0 || y < 0 || x > m - 1 || y > n - 1)
+                continue;
+            if(board[x][y] == 1 || board[x][y] == 2)
+                countLiveCell++;
+        }
+        if(board[i][j] == 0 && countLiveCell == 3)
+            board[i][j] = 3;
+        else if(board[i][j] == 1 && (countLiveCell < 2 || countLiveCell > 3)) {
+            board[i][j] = 2;
+        }
+    }
+
+}

MaxandMinOfArray.java

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+// Time Complexity : O(n) with n comparisons
+// Space Complexity : O(1)
+
+// Your code here along with comments explaining your approach
+/*
+Maintain min and max variables to track min and max values of array. now, compare consecutive elements to
+find min and max between them and assign them to min and max values if applicable.This way, we can avoid
+extra comparisons.This way, we can iterate every i+2 elements until end of array. To balance this check in
+odd length arrays, we initialize the iterating i pointer accordingly.
+ */
+public class MaxandMinOfArray {
+    public static int[] findMaxAndMin(int[] nums) {
+        int n = nums.length;
+        int min = Integer.MAX_VALUE;
+        int max = Integer.MIN_VALUE;
+        int i = 0;
+
+        if(n % 2 == 0) {
+            if(nums[0] < nums[1]) {
+                min = Math.min(min, nums[0]);
+                max = Math.max(max, nums[1]);
+            }
+            else {
+                min = Math.min(min, nums[1]);
+                max = Math.max(max, nums[0]);
+            }
+            i = 2;
+        }
+        else {
+            min = max = nums[0];
+            i = 1;
+        }
+        while(i < n - 1) {
+            if(nums[i] <  nums[i + 1]) {
+                min = Math.min(min, nums[i]);
+                max = Math.max(max, nums[i + 1]);
+            }
+            else {
+                min = Math.min(min, nums[i + 1]);
+                max = Math.max(max, nums[i]);
+            }
+            i = i + 2;
+        }
+        return new int[]{min, max};
+    }
+
+    public static void main(String[] args) {
+        int[] arr = new int[]{2, 3 , 1};
+        int[] minMax = findMaxAndMin(arr);
+        System.out.println("Minimum element is " + minMax[0] + " and maximum element is " + minMax[1]);
+    }
+}