From 633d0fc2872909b78886c343d4e6781670948180 Mon Sep 17 00:00:00 2001
From: Evan Ferrao <evanferrao@gmail.com>
Date: Wed, 14 Aug 2024 02:11:32 +0530
Subject: [PATCH] add array questions

> thats some crazy pascals triangle code
---
 Arrays/PascalsTriangle.java               | 100 ++++++++++++++++++++++
 Arrays/RotationMatrix.java                |  76 ++++++++++++++++
 Arrays/SpiralMatrixGeneration.java        |  61 +++++++++++++
 Arrays/SpiralMatrixTraversal.java         |  51 +++++++++++
 {Transpose => Arrays}/TansposeMatrix.java |   3 +-
 5 files changed, 289 insertions(+), 2 deletions(-)
 create mode 100644 Arrays/PascalsTriangle.java
 create mode 100644 Arrays/RotationMatrix.java
 create mode 100644 Arrays/SpiralMatrixGeneration.java
 create mode 100644 Arrays/SpiralMatrixTraversal.java
 rename {Transpose => Arrays}/TansposeMatrix.java (95%)

diff --git a/Arrays/PascalsTriangle.java b/Arrays/PascalsTriangle.java
new file mode 100644
index 0000000..0e0958b
--- /dev/null
+++ b/Arrays/PascalsTriangle.java
@@ -0,0 +1,100 @@
+// write a code in java to print the pascals triangle for a given number of rows using a function
+import java.util.Scanner;
+
+class PascalsTriangle{
+    public static void main(String[] args) {
+        Scanner sc = new Scanner(System.in);
+        System.out.println("Enter the number of rows: ");
+        int rows = sc.nextInt();
+        System.out.println("Pascal's Triangle: ");
+        // for(int i=0; i<rows; i++){
+        //     for(int j=0; j<=i; j++){
+        //         System.out.print(pascal(i, j) + " ");
+        //     }
+        //     System.out.println();
+        // }
+        //printPascalsTriangle(rows);
+        // int[][] memo = new int[rows][rows];
+        // for(int i=0; i<rows; i++){
+        //     for(int j=0; j<=i; j++){
+        //         System.out.print(pascalMemo(i, j, memo) + " ");
+        //     }
+        //     System.out.println();
+        // }
+        pascalDPSpaceOptimized(rows);
+        sc.close();     
+    }
+
+    public static void printPascalsTriangle(int rows){
+        for(int i=0; i<rows; i++){
+            int number = 1;
+            for(int j=0; j<=i; j++){
+                System.out.print(number + " ");
+                // proof using the formula nCr = n! / (r! * (n-r)!) [binomial coefficient]
+                number = number * (i-j) / (j+1);
+            }
+            System.out.println();
+        }
+    }
+
+    // write another function to print pasclas triangle using recursion
+    public static int pascal(int i, int j){
+        if(j == 0 || j == i){
+            return 1;
+        }
+        return pascal(i-1, j-1) + pascal(i-1, j);
+    }
+
+    // write another function to print pascals triangle using memoization
+    public static int pascalMemo(int i, int j, int[][] memo){
+        if(j == 0 || j == i){
+            return 1;
+        }
+        if(memo[i][j] != 0){
+            return memo[i][j];
+        }
+        memo[i][j] = pascalMemo(i-1, j-1, memo) + pascalMemo(i-1, j, memo);
+        return memo[i][j];
+    }
+
+    // write another function to print pascals triangle using dynamic programming
+    public static void pascalDP(int rows){
+        int[][] dp = new int[rows][rows];
+        for(int i=0; i<rows; i++){
+            for(int j=0; j<=i; j++){
+                if(j == 0 || j == i){
+                    dp[i][j] = 1;
+                }else{
+                    dp[i][j] = dp[i-1][j-1] + dp[i-1][j];
+                }
+            }
+        }
+        for(int i=0; i<rows; i++){
+            for(int j=0; j<=i; j++){
+                System.out.print(dp[i][j] + " ");
+            }
+            System.out.println();
+        }
+    }
+
+    // write another function to print pascals triangle using dynamic programming with space optimization
+    public static void pascalDPSpaceOptimized(int rows){
+        int[] dp = new int[rows];
+        for(int i=0; i<rows; i++){
+            for(int j=i; j>=0; j--){
+                if(j == 0 || j == i){
+                    dp[j] = 1;
+                }else{
+                    dp[j] = dp[j-1] + dp[j];
+                }
+            }
+
+            // does not save the entire triangle, only the current row
+            // its indented in the loop to print the triangle
+            for(int j=0; j<=i; j++){
+                System.out.print(dp[j] + " ");
+            }
+            System.out.println();
+        }
+    }
+}
\ No newline at end of file
diff --git a/Arrays/RotationMatrix.java b/Arrays/RotationMatrix.java
new file mode 100644
index 0000000..545361a
--- /dev/null
+++ b/Arrays/RotationMatrix.java
@@ -0,0 +1,76 @@
+// wrie a code in java to print the rotation matrix using the functions calculateRotation and calculateTranspose
+import java.util.Scanner;
+class RotationMatrix{
+        public static void main(String[] args) {
+        Scanner sc = new Scanner(System.in);
+        System.out.print("Enter the number of rows and columns: ");
+        int rows = sc.nextInt();
+        int columns = sc.nextInt();
+        int[][] matrix = new int[rows][columns];
+        System.out.println("Enter the elements of the matrix: ");
+        for(int i = 0; i < rows; i++){
+            for(int j = 0; j < columns; j++){
+                matrix[i][j] = sc.nextInt();
+            }
+        }
+        System.out.println("Original Matrix: ");
+        printMatrix(matrix);
+        System.out.println("Transpose Matrix: ");
+        printMatrix(calculateTranspose(matrix));
+        System.out.println("Rotation Matrix: ");
+        printMatrix(calculateRotation(matrix));
+        sc.close();
+    }
+    public static int[][] calculateTranspose(int[][] matrix){
+        int rows = matrix.length;
+        int columns = matrix[0].length;
+        int[][] transpose = new int[columns][rows];
+        for(int i = 0; i < rows; i++){
+            for(int j = 0; j < columns; j++){
+                transpose[j][i] = matrix[i][j];
+            }
+        }
+        return transpose;
+    }
+    public static int[][] calculateRotation(int[][] matrix){
+        int rows = matrix.length;
+        int columns = matrix[0].length;
+        int[][] rotation = new int[columns][rows];
+        for(int i = 0; i < rows; i++){
+            for(int j = 0; j < columns; j++){
+                rotation[j][rows - i - 1] = matrix[i][j];
+            }
+        }
+        return rotation;
+    }
+    public static void printMatrix(int[][] matrix){
+        for(int[] row : matrix){
+            for(int element : row){
+                System.out.print(element + " ");
+            }
+            System.out.println();
+        }
+    }
+
+    // calculate rotation from transpose
+
+    public static void reverseArray(int[] arr){
+        int start = 0;
+        int end = arr.length - 1;
+        while(start < end){
+            int temp = arr[start];
+            arr[start] = arr[end];
+            arr[end] = temp;
+            start++;
+            end--;
+        }
+    }
+    public static int[][] calculateRotationFromTranspose(int[][] matrix){
+        int transpose[][] =  calculateTranspose(matrix);
+        for (int i = 0; i < transpose.length; i++) {
+            reverseArray(transpose[i]);
+        }
+
+        return transpose;
+    }
+}
\ No newline at end of file
diff --git a/Arrays/SpiralMatrixGeneration.java b/Arrays/SpiralMatrixGeneration.java
new file mode 100644
index 0000000..0d8be67
--- /dev/null
+++ b/Arrays/SpiralMatrixGeneration.java
@@ -0,0 +1,61 @@
+// write a program to generate a n * n matrix in spiral order given user input n and the elements of the matrix
+
+import java.util.Scanner;
+class SpiralMatrixGeneration{
+
+    public static void main(String[] args){
+        Scanner sc = new Scanner(System.in);
+        System.out.println("Enter the number of rows and columns of the matrix");
+        int rows = sc.nextInt();
+        int cols = sc.nextInt();
+        int length = rows*cols;
+        int[][] matrix = new int[rows][cols];
+        int lengthArray[] = new int[length];
+        System.out.println("Enter the elements of the matrix");
+        for(int i=0;i<length;i++){
+            lengthArray[i] = sc.nextInt();
+        }
+        System.out.println("The elements of the matrix in spiral order are:");
+        spiralOrder(matrix,rows, cols, lengthArray);
+        for(int i=0;i<rows;i++){
+            for(int j=0;j<cols;j++){
+                System.out.print(matrix[i][j]+" ");
+            }
+            System.out.println();
+        }
+        sc.close();
+    }
+    public static void spiralOrder(int[][] matrix, int rows, int cols, int lengthArray[]){
+        int top = 0;
+        int bottom = rows-1;
+        int left = 0;
+        int right = cols-1;
+        int length_index = 0;
+        while(top<=bottom && left<=right){
+            // this loop does not need to check for the condition top<=bottom and left<=right as 
+            for(int i=left;i<=right;i++){
+
+                matrix[top][i] = lengthArray[length_index++];
+            }
+            top++;
+            // this loop does not need to check for the condition top<=bottom and left<=right as it is already checked in the while loop
+            for(int i=top;i<=bottom;i++){
+                matrix[i][right] = lengthArray[length_index++];
+            }
+            right--;
+            if(top<=bottom){
+                for(int i=right;i>=left;i--){
+                    matrix[bottom][i] = lengthArray[length_index++];
+                }
+                bottom--;
+            }
+            if(left<=right){
+                for(int i=bottom;i>=top;i--){
+                    matrix[i][left] = lengthArray[length_index++];
+                }
+                left++;
+            }
+        }
+    }
+
+}
\ No newline at end of file
diff --git a/Arrays/SpiralMatrixTraversal.java b/Arrays/SpiralMatrixTraversal.java
new file mode 100644
index 0000000..de2e6f0
--- /dev/null
+++ b/Arrays/SpiralMatrixTraversal.java
@@ -0,0 +1,51 @@
+// write a code in java to print the elements in a matrix in a spiral order using functions
+
+import java.util.Scanner;
+class SpiralMatrixTraversal{
+    public static void main(String[] args){
+        Scanner sc = new Scanner(System.in);
+        System.out.println("Enter the number of rows and columns of the matrix");
+        int rows = sc.nextInt();
+        int cols = sc.nextInt();
+        int[][] matrix = new int[rows][cols];
+        System.out.println("Enter the elements of the matrix");
+        for(int i=0;i<rows;i++){
+            for(int j=0;j<cols;j++){
+                matrix[i][j] = sc.nextInt();
+            }
+        }
+        System.out.println("The elements of the matrix in spiral order are:");
+        spiralOrder(matrix,rows,cols);
+        sc.close();
+    }
+    public static void spiralOrder(int[][] matrix, int rows, int cols){
+        int top = 0;
+        int bottom = rows-1;
+        int left = 0;
+        int right = cols-1;
+        while(top<=bottom && left<=right){
+            // this loop does not need to check for the condition top<=bottom and left<=right as 
+            for(int i=left;i<=right;i++){
+                System.out.print(matrix[top][i]+" ");
+            }
+            top++;
+            // this loop does not need to check for the condition top<=bottom and left<=right as it is already checked in the while loop
+            for(int i=top;i<=bottom;i++){
+                System.out.print(matrix[i][right]+" ");
+            }
+            right--;
+            if(top<=bottom){
+                for(int i=right;i>=left;i--){
+                    System.out.print(matrix[bottom][i]+" ");
+                }
+                bottom--;
+            }
+            if(left<=right){
+                for(int i=bottom;i>=top;i--){
+                    System.out.print(matrix[i][left]+" ");
+                }
+                left++;
+            }
+        }
+    }
+}
\ No newline at end of file
diff --git a/Transpose/TansposeMatrix.java b/Arrays/TansposeMatrix.java
similarity index 95%
rename from Transpose/TansposeMatrix.java
rename to Arrays/TansposeMatrix.java
index 1da3ba4..d489475 100644
--- a/Transpose/TansposeMatrix.java
+++ b/Arrays/TansposeMatrix.java
@@ -45,7 +45,7 @@ calss TransposeMatrix {
         return result;
     }
 
-    public static int[][] transposeOriginalMatrix(int[][] matrix) {
+    public static void transposeOriginalMatrix(int[][] matrix) {
         int rows = matrix.length;
         int cols = matrix[0].length;
         for (int i = 0; i < rows; i++) {
@@ -55,6 +55,5 @@ calss TransposeMatrix {
                 matrix[j][i] = temp;
             }
         }
-        return matrix;
     }
 }
\ No newline at end of file