Implement Array-1: Self Product,and Diagonal and Spiral Matrix

DiagonalMatrix.java

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+// Time Complexity :O(M*N)
+// Space Complexity : O(1) without considering result space.
+// Did this code successfully run on Leetcode : Yes
+// Three line explanation of solution in plain english
+
+// Your code here along with comments explaining your approach
+
+class DiagonalMatrix {
+    public int[] findDiagonalOrder(int[][] matrix) {
+        if (matrix == null) {
+            throw new IllegalArgumentException("Input matrix is null");
+        }
+        if (matrix.length == 0 || matrix[0].length == 0) {
+            return new int[0];
+        }
+
+        int rows = matrix.length;
+        int cols = matrix[0].length;
+        int[] result = new int[rows * cols];
+        int r = 0;
+        int c = 0;
+        boolean up = true;
+
+        for (int i = 0; i < result.length; i++) {
+            result[i] = matrix[r][c];
+            if(up) { // Move Up
+                if (c == cols - 1) {
+                    // Reached last column. Now move to below cell in the same column.
+                    // This condition needs to be checked first due to top right corner cell.
+                    r++;
+                    up=false;
+                } else if (r == 0) {
+                    // Reached first row. Now move to next cell in the same row.
+                    c++;
+                    up=false;
+                } else {
+                    // Somewhere in middle. Keep going up diagonally.
+                    r--;
+                    c++;
+                }
+            } else { // Move Down
+                if (r == rows - 1) {
+                    // Reached last row. Now move to next cell in same row.
+                    // This condition needs to be checked first due to bottom left corner cell.
+                    c++;
+                    up=true;
+                } else if (c == 0) {
+                    // Reached first columns. Now move to below cell in the same column.
+                    r++;
+                    up=true;
+                } else {
+                    // Somewhere in middle. Keep going down diagonally.
+                    r++;
+                    c--;
+                }
+            }
+        }
+
+        return result;
+    }
+}

Product.java

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+// Time Complexity : O(n)
+// Space Complexity : O(1)
+// Did this code successfully run on Leetcode : Yes
+// Three line explanation of solution in plain english
+/*Calculate the product on the left of all the numbers in the array.
+Going from right to left calculate the product on the right of the number and multiply with the product obtained before at each position
+*/
+
+// Your code here along with comments explaining your approach
+
+/*
+## Problem 1 - Leetcode 238.Product of Array Except Self
+
+ */
+
+class Product {
+
+    public int[] productExceptSelf(int[] nums) {
+        int[] result = new int[nums.length];
+
+        int[] leftProduct = new int[nums.length];
+        result[0] = 1;
+
+        for (int i = 1; i < nums.length; i++) {
+            result[i] = result[i - 1] * nums[i - 1];
+        }
+
+        int rightProduct = 1;
+        for (int i = nums.length - 2; i >= 0; i--) {
+            rightProduct *= nums[i + 1];
+            result[i] = result[i] * rightProduct;
+        }
+
+        return result;
+
+    }
+}

SpiralMatrix.java

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+// Time Complexity : O(m*n)
+// Space Complexity : O(1)
+// Did this code successfully run on Leetcode : Yes
+// Three line explanation of solution in plain english
+//Take four pointers ->left, top, right, and bottom.
+//And navigate left to right, top to bottom, right to left, bottom to top in that order.
+//Increase or decrease the pointers accordingly.
+
+// Your code here along with comments explaining your approach
+class SpiralMatrix {
+    public List<Integer> spiralOrder(int[][] matrix) {
+        List<Integer> result = new ArrayList<>();
+
+        int m = matrix.length;
+        int n = matrix[0].length;
+
+        int left = 0;
+        int top = 0;
+        int right = n - 1;
+        int bottom = m - 1;
+
+        while (left <= right && top <= bottom) {
+
+            for (int j = left; j <= right; j++) {
+                result.add(matrix[top][j]);
+            }
+            top++;
+
+
+            for (int i = top; i <= bottom; i++) {
+                result.add(matrix[i][right]);
+            }
+            right--;
+
+
+            if (top <= bottom) {
+                for (int j = right; j >= left; j--) {
+                    result.add(matrix[bottom][j]);
+                }
+                bottom--;
+            }
+
+            if (left <= right) {
+                for (int i = bottom; i >= top; i--) {
+                    result.add(matrix[i][left]);
+                }
+                left++;
+            }
+
+        }
+
+        return result;
+
+    }
+}