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Matrices

  • Understanding matrices
  • Solved problems are presented in alphabetical order
Flood Fill
Spiral Matrix

↗ See LeetCode Problem #54​

import java.util.List;import java.util.ArrayList;public class Solution {    public static List<Integer> spiralOrder(int[][] matrix) {        List<Integer> elementsSpiralOrder = new ArrayList<>();        int topBoundary = 0;        int leftBoundary = 0;        //  matrix[0].length gives number of columns        int rightBoundary = matrix[0].length - 1;        //  matrix.length gives number of rows        int bottomBoundary = matrix.length - 1;        while (elementsSpiralOrder.size() <                matrix.length * matrix[0].length) {            //  Add elements in the top row (moving left to right)            for (int i = leftBoundary; i <= rightBoundary; i++) {                elementsSpiralOrder.add(matrix[topBoundary][i]);            }            //  Add elements in the right column (moving downwards)            for (int i = topBoundary + 1; i <= bottomBoundary; i++) {                elementsSpiralOrder.add(matrix[i][rightBoundary]);            }            //  Check topBoundary is not same as bottomBoundary            if (topBoundary < bottomBoundary) {                //  Add elements in the bottom row (moving right to left)                for (int i = rightBoundary - 1; i >= leftBoundary; i--) {                    elementsSpiralOrder.add(matrix[bottomBoundary][i]);                }            }            //  Check rightBoundary is not same as leftBoundary            if (leftBoundary < rightBoundary) {                //  Add elements in the left column (moving upwards)                //  i > topBoundary because                //      topBoundary element has already been added                //      unlike elements in the for loops above this for loop                for (int i = bottomBoundary - 1; i > topBoundary; i--) {                    elementsSpiralOrder.add(matrix[i][leftBoundary]);                }            }            leftBoundary++;            topBoundary++;            rightBoundary--;            bottomBoundary--;        }        return elementsSpiralOrder;    }    public static void main(String[] args) {        // Example 1:        int[][] matrix1 = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};        //  O/P: [1,2,3,6,9,8,7,4,5]        // Example 2:        int[][] matrix2 = {{1, 2, 3, 4}, {5, 6, 7, 8}, {9, 10, 11, 12}};        //  O/P: [1,2,3,4,8,12,11,10,9,5,6,7]        System.out.println(spiralOrder(matrix1));        System.out.println(spiralOrder(matrix2));    }}
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