Array-2 solutions

FindAllNumbersMissingInArray.java

@@ -0,0 +1,26 @@
+// Time Complexity : O(n).
+// Space Complexity : O(1)
+// Did this code successfully run on Leetcode : Yes
+// Approach : If we sort the Array, as the condition is 1 to n numbers, the element should be at i+1 index. Assuming this logic, we
+// iterate through array and make the index's value-1 index to be negative. Which means all the numbers already present will be negative.
+// Now we iterate again, and the index+1 of the positive numbers ill give the result.
+
+class Solution {
+    public List<Integer> findDisappearedNumbers(int[] nums) {
+        List<Integer> res = new ArrayList<>();
+
+        for(int i=0;i<nums.length;i++){
+            int val = Math.abs(nums[i]);
+            if(nums[val-1] > 0){
+                nums[val-1] = -nums[val-1]; //marking the value that is supposed to be in this position to negative
+            }
+        }
+
+        for(int i=0;i<nums.length;i++){
+            if(nums[i] > 0){ //non-negative number's index will be the ones that are not visited.
+                res.add(i+1);
+            }
+        }
+        return res;
+    }
+}

GameOfLife.java

@@ -0,0 +1,54 @@
+// Time Complexity : O(m*n).
+// Space Complexity : O(1)
+// Did this code successfully run on Leetcode : Yes
+// Approach : As per the problem and given conditions, we change the alive to dead ones to 2 and dead to alive ones to 3. As all
+// operations happen simultaneously according to the problem, we shouldn't consider the updated values so we maintain 2 or 3 for updated
+// ones. We first calculate the alives and perform the logic on the count, iterate the array again and transform 2 and 3 to alive or
+// dead values in the matrix.
+
+class Solution {
+    int m, n;
+
+    public void gameOfLife(int[][] board) {
+        this.m = board.length;
+        this.n = board[0].length;
+        for (int i=0;i<m;i++){
+            for(int j=0;j<n;j++){
+                int alivesCount = CountAlives(board, i, j);
+                if(board[i][j] == 1 && (alivesCount < 2 || alivesCount > 3)){ //as per the condition in problem
+                    board[i][j] = 2; // alive to dead.
+                }
+                if(board[i][j] == 0 && alivesCount == 3){
+                    board[i][j] = 3;// dead to alive
+                }
+            }
+
+        }
+        for(int i=0; i<m; i++){
+            for(int j=0; j<n; j++){// iterate again to make 2's as 0 and 3 as 1
+                if(board[i][j] == 2){
+                    board[i][j] = 0;
+                }else if(board[i][j] == 3){
+                    board[i][j] = 1;
+                }
+            }
+        }
+
+    }
+
+    public int CountAlives(int[][] board, int i, int j) {
+        //All 8 possible directions are stored.
+        int directions[][] = { { -1, -1 }, { -1, 0 }, { -1, 1 }, { 0, 1 }, { 0, -1 }, { 1, -1 }, { 1, 0 }, { 1, 1 } };
+        int count = 0;
+        for (int[] dir : directions) {
+            int row = i + dir[0];
+            int col = j + dir[1];
+
+            if (row >= 0 && row < m && col >= 0 && col < n) { // row and column are within borders.
+                if (board[row][col] == 1 || board[row][col] == 2) //as we changed to 2 for alive to dead.
+                    count++;
+            }
+        }
+        return count;
+    }
+}

MinAndMaxInArray.java

@@ -0,0 +1,33 @@
+// Time Complexity : O(n).
+// Space Complexity : O(1)
+// Did this code successfully run on Leetcode : Yes
+// Approach : Comparison by pairs approach helps in reducing the comparisons that checking min and max at each value. We consider two
+// elements in the array and based on the bigger value we compare with existing max and voce versa for min. If array size is odd I was
+// missing the last element, so I have added an additional condition for it as well.
+
+class Solution {
+    public ArrayList<Integer> getMinMax(int[] arr) {
+        // code Here
+        ArrayList<Integer> res = new ArrayList<>();
+        int min = Integer.MAX_VALUE;
+        int max = Integer.MIN_VALUE;
+        int i=0;
+        for(i=0;i<arr.length-1;i+=2){ //increment by 2 as we are comparing pairs
+            if(arr[i] < arr[i+1]){
+                min = Math.min(min,arr[i]);
+                max = Math.max(max,arr[i+1]); //as i+1 is bigger, compare with previous max
+            } else{
+                min = Math.min(min,arr[i+1]); //as i+1 is smaller, compare with previous min
+                max = Math.max(max,arr[i]);
+            }
+        }
+        if(i == arr.length-1){ //additional check for last element of odd length arrays
+            min = Math.min(min,arr[i]);
+            max = Math.max(max,arr[i]);
+        }
+        res.add(min);
+        res.add(max);
+        return res;
+
+    }
+}