Code Patterns Flutter / Dart

sliding_window.dart

import 'package:flutter/material.dart';
import 'dart:math';

void main() => runApp(const MyApp());

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Design Pattern Demo',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const SlidingWindowScreen(),
    );
  }
}

class SlidingWindowScreen extends StatefulWidget {
  const SlidingWindowScreen({Key? key}) : super(key: key);

  @override
  SlidingWindowScreenState createState() => SlidingWindowScreenState();
}

class SlidingWindowScreenState extends State<SlidingWindowScreen>
    with SingleTickerProviderStateMixin {
  List<int> numbers = [];
  final int k = 3;
  late AnimationController _animationController;
  late Animation<Offset> _animation;
  List<int> maxSumElements = [];

  @override
  void initState() {
    super.initState();
    generateNumbers();
    _animationController = AnimationController(
      vsync: this,
      duration: const Duration(milliseconds: 500),
    );
    _animation = Tween<Offset>(begin: Offset.zero, end: const Offset(0.0, 1.0))
        .animate(_animationController);
  }

  @override
  void dispose() {
    _animationController.dispose();
    super.dispose();
  }

  void generateNumbers() {
    final random = Random();
    numbers = List.generate(10, (_) => random.nextInt(10));
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Sliding Window - bwnyasse.net'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            const Text(
              'Numbers:',
              style: TextStyle(fontSize: 18),
            ),
            const SizedBox(height: 10),
            buildNumberList(),
            const SizedBox(height: 20),
            SlideTransition(
              position: _animation,
              child: Text(
                'Max Sum of $k Consecutive Elements: ${findMaxSum()}',
                style:
                    const TextStyle(fontSize: 24, fontWeight: FontWeight.bold),
              ),
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          setState(() {
            generateNumbers();
            maxSumElements.clear();
          });
        },
        child: const Icon(Icons.play_arrow),
      ),
    );
  }

  Widget buildNumberList() {
    return SizedBox(
      height: 40,
      child: ListView.builder(
        shrinkWrap: true,
        scrollDirection: Axis.horizontal,
        itemCount: numbers.length,
        itemBuilder: (BuildContext context, int index) {
          final color =
              maxSumElements.contains(index) ? Colors.green : Colors.blue;
          return Container(
            width: 40,
            height: 40,
            margin: const EdgeInsets.symmetric(horizontal: 4),
            decoration: BoxDecoration(
              color: color,
              borderRadius: BorderRadius.circular(8),
            ),
            child: Center(
              child: Text(
                numbers[index].toString(),
                style: const TextStyle(color: Colors.white),
              ),
            ),
          );
        },
      ),
    );
  }

  int findMaxSum() {
    int maxSum = 0;
    int currentSum = 0;
    int maxSumIndex = 0;

    // Calculate sum of first 'k' elements
    for (int i = 0; i < k; i++) {
      currentSum += numbers[i];
    }

    maxSum = currentSum;

    // Slide the window by one element at a time
    for (int i = k; i < numbers.length; i++) {
      currentSum = currentSum - numbers[i - k] + numbers[i];
      if (currentSum > maxSum) {
        maxSum = currentSum;
        maxSumIndex = i - k + 1;
      }
    }

    maxSumElements = List<int>.generate(k, (index) => maxSumIndex + index);

    return maxSum;
  }
}

the_islands.dart

import 'package:flutter/material.dart';
import 'dart:math';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: IslandsScreen(),
    );
  }
}

class IslandsScreen extends StatefulWidget {
  @override
  _IslandsScreenState createState() => _IslandsScreenState();
}

class _IslandsScreenState extends State<IslandsScreen> {
  List<List<int>> grid = [];
  int numIslands = 0;

  @override
  void initState() {
    super.initState();
    generateGrid();
    countIslands();
  }

  void generateGrid() {
    final random = Random();
    final numRows =  3;
    final numCols = 3;

    grid = List.generate(
        numRows, (_) => List.generate(numCols, (_) => random.nextInt(2)));
  }

  void countIslands() {
    numIslands = 0;

    if (grid.isEmpty) {
      return;
    }

    final int rows = grid.length;
    final int cols = grid[0].length;
    final List<List<bool>> visited = List.generate(
      rows,
      (_) => List<bool>.filled(cols, false),
    );

    for (int i = 0; i < rows; i++) {
      for (int j = 0; j < cols; j++) {
        if (grid[i][j] == 1 && !visited[i][j]) {
          numIslands++;
          dfs(i, j, visited);
        }
      }
    }
  }

  void dfs(int row, int col, List<List<bool>> visited) {
    final int rows = grid.length;
    final int cols = grid[0].length;

    if (row < 0 ||
        row >= rows ||
        col < 0 ||
        col >= cols ||
        grid[row][col] == 0 ||
        visited[row][col]) {
      return;
    }

    visited[row][col] = true;

    // Explore neighbors in all four directions
    dfs(row - 1, col, visited); // Up
    dfs(row + 1, col, visited); // Down
    dfs(row, col - 1, visited); // Left
    dfs(row, col + 1, visited); // Right
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Islands'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Text(
              'Number of Islands: $numIslands',
              style: TextStyle(fontSize: 24, fontWeight: FontWeight.bold),
            ),
            SizedBox(height: 20),
            GridView.builder(
              shrinkWrap: true,
              gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
                crossAxisCount: grid[0].length,
                mainAxisSpacing: 4,
                crossAxisSpacing: 4,
              ),
              itemCount: grid.length * grid[0].length,
              itemBuilder: (BuildContext context, int index) {
                final int row = index ~/ grid[0].length;
                final int col = index % grid[0].length;
                final int value = grid[row][col];

                return Container(
                  color: value == 1 ? Colors.blue : Colors.white,
                  child: Center(
                    child: Text(
                      value.toString(),
                      style: TextStyle(
                        color: value == 1 ? Colors.white : Colors.black,
                        fontWeight: FontWeight.bold,
                      ),
                    ),
                  ),
                );
              },
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          setState(() {
            generateGrid();
            countIslands();
          });
        },
        child: Icon(Icons.refresh),
      ),
    );
  }
}

two_pointers.dart

// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

import 'package:flutter/material.dart';
import 'dart:math';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: TwoPointersScreen(),
    );
  }
}

class TwoPointersScreen extends StatefulWidget {
  @override
  _TwoPointersScreenState createState() => _TwoPointersScreenState();
}

class _TwoPointersScreenState extends State<TwoPointersScreen> {
  List<int> numbers = [];
  int target = 0;
  bool isPairFound = false;
  int leftPointer = -1;
  int rightPointer = -1;

  @override
  void initState() {
    super.initState();
    generateInput();
    findPair();
  }

  void generateInput() {
    final random = Random();
    final numSet = Set<int>();

    while (numSet.length < 10) {
      numSet.add(random.nextInt(30));
    }

    numbers = numSet.toList();
    target = random.nextInt(70);
  }

  void findPair() {
    isPairFound = false;
    leftPointer = -1;
    rightPointer = -1;
    int left = 0;
    int right = numbers.length - 1;
    numbers.sort(); // Sorting the numbers to use the Two Pointers pattern

    while (left < right) {
      final int sum = numbers[left] + numbers[right];
      if (sum == target) {
        isPairFound = true;
        leftPointer = left;
        rightPointer = right;
        break;
      } else if (sum < target) {
        left++;
      } else {
        right--;
      }
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Two Pointers'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Text(
              'Numbers:',
              style: TextStyle(fontSize: 18),
            ),
            SizedBox(height: 10),
            buildNumberList(),
            SizedBox(height: 10),
            Text(
              'Target: $target',
              style: TextStyle(fontSize: 18),
            ),
            SizedBox(height: 20),
            Text(
              'Pair Found: ${isPairFound ? "Yes" : "No"}',
              style: TextStyle(fontSize: 24, fontWeight: FontWeight.bold),
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          setState(() {
            generateInput();
            findPair();
          });
        },
        child: Icon(Icons.refresh),
      ),
    );
  }

  Widget buildNumberList() {
    return Wrap(
      spacing: 4,
      runSpacing: 4,
      children: numbers.map((number) {
        final isHighlighted =
            (numbers[leftPointer] == number || numbers[rightPointer] == number);
        final color = isHighlighted ? Colors.green : Colors.blue;

        return Container(
          width: 40,
          height: 40,
          decoration: BoxDecoration(
            color: color,
            borderRadius: BorderRadius.circular(8),
          ),
          child: Center(
            child: Text(
              number.toString(),
              style: TextStyle(color: Colors.white),
            ),
          ),
        );
      }).toList(),
    );
  }
}