Day12 - game-of-life, find-all-numbers-disappeared-in-an-array, min-max

Find-all-numbers-disappeared-in-an-array.java

@@ -0,0 +1,22 @@
+class Solution {
+    public List<Integer> findDisappearedNumbers(int[] nums) {
+        int m = nums.length;
+        List<Integer> list = new ArrayList<>();
+        for(int j=0;j<m;j++){
+            int x = Math.abs(nums[j]);
+            int y = nums[x-1];
+            if(y>0){
+                nums[x-1] *= -1;
+            }
+
+        }
+        for(int j=0;j<m;j++){
+            if(nums[j]>0){
+                list.add(j+1); //add the indices
+            }else{
+                nums[j] *= -1; //make the -ve elements as before to return as the original array
+            }
+        }
+        return list;
+    }
+}

Game-of-life.java

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+class Solution {
+    //1. 1-> <2 -> 0 ---2
+    //2. 1-> 2or3 -> 1
+    //3. 1-> >3 -> 0 --2
+    //4. 0-> ==3 -> 1 ---3
+    public void gameOfLife(int[][] board) {
+        int m = board.length;
+        int n = board[0].length;
+        int[][] dirs = new int[][]{{-1,0},{1,0},{0,-1},{0,1},{-1,-1},{-1,1},{1,1},{1,-1}};
+        for(int i=0;i<m;i++){
+            for(int j=0;j<n;j++){
+                int countAlives = countLives(board, dirs, i,j,m,n);
+                if(board[i][j] == 0 && countAlives == 3){
+                    board[i][j] = 3;
+                }
+                if(board[i][j] == 1 && (countAlives < 2 || countAlives > 3)){
+                    board[i][j] = 2;
+                }
+            }
+        }
+        for(int i=0;i<m;i++){
+            for(int j=0;j<n;j++){
+                if(board[i][j]==2){
+                    board[i][j] = 0; //new state
+                }else if(board[i][j]==3){
+                    board[i][j] = 1; //new state
+                }
+            }
+
+        }
+
+    }
+    private int countLives(int[][] board, int[][] dirs, int i, int j, int m, int n){
+        int count = 0;
+        for(int[] dir:dirs){
+            int nr = i + dir[0];
+            int nc = j + dir[1];
+            if(nr>=0 && nc>=0 && nr<m && nc<n && (board[nr][nc]==1 || board[nr][nc]==2)){
+                count++;
+            }
+        }
+        return count;
+    }
+}

Minimum-and-maximum.java

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+class Solution {
+    public int[] minMax(int[] nums){
+        min = Integer.MAX_VALUE;
+        max = Integer.MIN_VALUE;
+        for(int i=0;i<n-2;i+2){
+            if(nums[i]> nums[i+1]){
+                min = Math.min(min, nums[i+1]);
+                max = Math.max(max, nums[i]);
+            }else{
+                min = Math.min(min, nums[i]);
+                max = Math.max(max, nums[i+1]);
+            }
+        }
+        return new int[]{min, max};
+    }
+}

README.md

@@ -1,10 +1,19 @@
 # Array-2
 
 ## Problem1 (https://leetcode.com/problems/find-all-numbers-disappeared-in-an-array/)
-
+* nums that are not there need to be return
+* Bruteforce - boolean array. Whichever element is present, value is True, else it is False. But it is taking additional space. To avoid that use optimal approach.
+* Optimal - Use Temporaray state pattern, whichever element is present, at what index that element would be present make it -ve. If it was already -ve take absolute value of that, then change to -ve. If its duplicate element, don't do anything,  Let the -ve be -ve only.
 
 ## Problem2
 Given an array of numbers of length N, find both the minimum and maximum. Follow up : Can you do it using less than 2 * (N - 2) comparison
+* Bruteforce - check every element, it will have 2n comparisons.
+* Optimal consider pair, from that pair choose min & max. Do it for N/2 pairs. it will have N-2 comparison for min  & N-2 for max
+
 
 ## Problem3 (https://leetcode.com/problems/game-of-life/)
+* Bruteforce - we need to maintain extra apace for original state.
+* Optimal - 1st & 4th condition where states are changing use  Temporaray state pattern. Ex- 1-> <2 -> 0 ---2, 1-> >3 -> 0 --2, 0-> ==3 -> 1 ---3
+* func countLives - to count 1s in all 8 directions
+