leet code problems

Author: techie-khushdeep

src/leetcode/array/Q977.java

@@ -0,0 +1,34 @@
+package leetcode.array;
+
+import java.util.Arrays;
+
+//square of sorted array with two pointer approach
+// space o(n)
+// time o(n);
+//https://leetcode.com/problems/squares-of-a-sorted-array/
+public class Q977 {
+    public static int[] sortedSquares(int[] nums) {
+        int n = nums.length;
+        int[] result = new int[nums.length];
+        int left = 0;
+        int right = nums.length-1;
+        for(int i=n-1;i>=0;i--){
+            int square;
+            if(Math.abs(nums[left])>Math.abs(nums[right])){
+                square = nums[left];
+                left++;
+            }else{
+                square = nums[right];
+                right--;
+            }
+            result[i]= square * square;
+        }
+        return result;
+    }
+
+    public static void main(String[] args) {
+        int[] nums = {-7,-3,2,3,11};
+        int[] result = sortedSquares(nums);
+        System.out.println(Arrays.toString(result));
+    }
+}

src/recursion/NQueenProblem.java

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+package recursion;
+
+import java.util.Arrays;
+
+public class NQueenProblem {
+    public static void main(String[] args) {
+        int n=8;
+        boolean[][] board = new boolean[n][n];
+        System.out.println(getSolution(board,0));
+    }
+    public static int getSolution(boolean[][] board,int row){
+        if(row== board.length){
+            display(board);
+            System.out.println();
+            return 1;
+        }
+        int count=0;
+        //first place the queen
+        for (int i=0;i<board[0].length;i++){
+
+            if(isSafe(board,row,i)){
+                board[row][i]=true;
+                count += getSolution(board,row+1);
+                board[row][i]=false;
+            }
+
+        }
+        return count;
+    }
+    public static void display(boolean[][] board){
+        for (boolean[] row:board){
+            for (boolean col: row){
+                if(col){
+                    System.out.print("Q ");
+                }else{
+                    System.out.print("X ");
+                }
+            }
+            System.out.println();
+        }
+    }
+    public static boolean isSafe(boolean[][] board,int row,int col){
+        //vertical
+        for(int i=0;i<row;i++){
+            if(board[i][col]){
+                return false;
+            }
+        }
+        //left diagonal
+        int minStep = Math.min(row,col);
+        for(int i=1;i<minStep;i++){
+            if(board[row-i][col-i]){
+                return false;
+            }
+        }
+        //right diagonal
+        minStep = Math.min(row,board[0].length-1-col);
+        for(int i=0;i<minStep;i++){
+            if(board[row-i][col+i]){
+                return false;
+            }
+        }
+        return true;
+    }
+}