CSA Blog
Ian Wu
Unit 4.4 - Nested Iteration
 |
4.1 While Loop | 4.2 For Loop | 4.3 String Iteration | 4.4 Nested Iteration | Unit 4 HW Quiz |
4.4 Nested Iteration
How to iterate through with a time complexity of O(n^2)
for (int i = 1; i <= 3; i++) { // Outer loop
System.out.println("Outer loop iteration: " + i);
for (int j = 1; j <= 3; j++) { // Inner loop
System.out.println(" Inner loop iteration: " + j);
}
}
Outer loop iteration: 1
Inner loop iteration: 1
Inner loop iteration: 2
Inner loop iteration: 3
Outer loop iteration: 2
Inner loop iteration: 1
Inner loop iteration: 2
Inner loop iteration: 3
Outer loop iteration: 3
Inner loop iteration: 1
Inner loop iteration: 2
Inner loop iteration: 3
What is wrong with this code cell(Hack)
//Hint: Check the Syntax and look at the equals to signs on the example above
import java.util.Scanner;
Scanner scanner = new Scanner(System.in);
System.out.print("Enter the number of rows: \n");
int rows = scanner.nextInt();
for (int i = rows; i >+ 1; i--) {
for (int j = 1; j <= i; j++) {
System.out.print(j + " ");
}
System.out.println();
}
scanner.close();
Enter the number of rows:
1 2 3 4 5
1 2 3 4
1 2 3
1 2
Sample input: 5
Sample Output 1 2 3 4 5 1 2 3 4 1 2 3 1 2 1
Answer here + One sentence Explanation
Answer here + One sentence Explanation
Video To watch later if you need more help
Cool Usecase of nested loops
// Define the dimensions
int rows = 5;
// First loop to generate a diamond pattern
System.out.println("Diamond Pattern:");
for (int i = 1; i <= rows; i++) {
// Print spaces for left alignment
for (int j = i; j < rows; j++) {
System.out.print(" ");
}
// Print asterisks for the upper part of the diamond
for (int k = 1; k <= (2 * i - 1); k++) {
System.out.print("*");
}
System.out.println();
}
for (int i = rows - 1; i >= 1; i--) {
// Print spaces for right alignment
for (int j = rows; j > i; j--) {
System.out.print(" ");
}
// Print asterisks for the lower part of the diamond
for (int k = 1; k <= (2 * i - 1); k++) {
System.out.print("*");
}
System.out.println();
}
// Second loop: Magic Square (Latin Square)
System.out.println("\nMagic Square (Latin Square):");
int size = 4;
int[][] magicSquare = new int[size][size];
int num = 1, row = 0, col = size / 2;
while (num <= size * size) {
magicSquare[row][col] = num;
num++;
int newRow = (row - 1 + size) % size;
int newCol = (col + 1) % size;
if (magicSquare[newRow][newCol] != 0) {
row = (row + 1) % size;
} else {
row = newRow;
col = newCol;
}
}
// Print the magic square
for (int[] r : magicSquare) {
for (int c : r) {
System.out.print(c + "\t");
}
System.out.println();
}
// Third loop: Prime Number Spiral
System.out.println("\nPrime Number Spiral:");
int spiralSize = 5;
int[][] spiral = new int[spiralSize][spiralSize];
int val = 1, startRow = 0, endRow = spiralSize - 1, startCol = 0, endCol = spiralSize - 1;
while (startRow <= endRow && startCol <= endCol) {
// Fill top row
for (int i = startCol; i <= endCol; i++) {
spiral[startRow][i] = isPrime(val) ? val : 0;
val++;
}
startRow++;
// Fill right column
for (int i = startRow; i <= endRow; i++) {
spiral[i][endCol] = isPrime(val) ? val : 0;
val++;
}
endCol--;
// Fill bottom row
if (startRow <= endRow) {
for (int i = endCol; i >= startCol; i--) {
spiral[endRow][i] = isPrime(val) ? val : 0;
val++;
}
endRow--;
}
// Fill left column
if (startCol <= endCol) {
for (int i = endRow; i >= startRow; i--) {
spiral[i][startCol] = isPrime(val) ? val : 0;
val++;
}
startCol++;
}
}
// Print the spiral
for (int[] r : spiral) {
for (int c : r) {
System.out.print(c + "\t");
}
System.out.println();
}
// Method to check if a number is prime
static boolean isPrime(int num) {
if (num <= 1) return false;
for (int i = 2; i <= Math.sqrt(num); i++) {
if (num % i == 0) return false;
}
return true;
}
Diamond Pattern:
*
***
*****
*******
*********
*******
*****
***
*
Magic Square (Latin Square):
9 15 1 7
14 4 6 12
3 5 11 13
8 10 16 2
Prime Number Spiral:
0 2 3 0 5
0 17 0 19 0
0 0 0 0 7
0 23 0 0 0
13 0 11 0 0
2
15
15
Iteration: 0
Current Velocity: 2, 2
Unit_4.3_ipynb_2_.md:zone
Unit 4.3 - String Iteration
|
4.1 While Loop | 4.2 For Loop | 4.3 String Iteration | 4.4 Nested Iteration | Unit 4 HW Quiz |
4.3 String Iteration
simple for loop to iterate through every character using index with charAt():
String word = "hello";
for (int i = 0; i < word.length(); i++) {
System.out.println(word.charAt(i));
}
in order to use an enhanced for loop, a character array is needed.
toCharArray() can help accomplish this.
example of iteration with an enhanced for loop:
String word = "hello";
for (char c : word.toCharArray()) {
System.out.println(c);
}
Popcorn Hack:
Iterate through the characters a string with a while loop
String string = "qwertyuioplkjhgfdsazxcvbnm";
int i = 0;
while (i < string.length()) {
System.out.println(string.charAt(i));
i += 1;
}
q
w
e
r
t
y
u
i
o
p
l
k
j
h
g
f
d
s
a
z
x
c
v
b
n
m
What is a substring?
- a substring is a subset of the main string
- the substring(a,b) method creates a substring with the characters of the original string with indices of a to b.
- string.length() returns the length of the string
- string1.equals(string2) determines if the two strings have the same characters
String word = "sunflower";
String sub = "low";
boolean found = false;
for (int i = 0; i < word.length(); i++) {
String portion = word.substring(i, i+sub.length());
if (portion.equals(sub)){
found = true;
}
}
System.out.println("is " + )
Iterating through words
use split() to split a string into an array.
then we can iterate through the array to access each individual word
String phrase = "this is a string";
String[] words = phrase.split(" ");
for (String word : words) {
System.out.println(word);
}
Homework Hack!
code a caesar cipher that will encrypt any string with any key provided.
your code should go into the encrypt() method, and should successfully pass the test cases provided
as a bonus, try to use StringBuilder
public class CaesarCipher {
private int key;
private String phrase;
public CaesarCipher(int key, String phrase) {
this.key = key;
this.phrase = phrase;
}
public String encrypt() {
StringBuilder encryptedPhrase = new StringBuilder();
for (char letter : this.phrase.toCharArray()) {
if (Character.isLetter(letter)) {
char base = Character.isUpperCase(letter) ? 'A' : 'a';
char shiftedLetter = (char) ((letter - base + this.key) % 26 + base);
encryptedPhrase.append(shiftedLetter);
} else {
encryptedPhrase.append(letter);
}
}
return encryptedPhrase.toString();
}
}
CaesarCipher test1 = new CaesarCipher(3, "hello world");
CaesarCipher test2 = new CaesarCipher(10, "abcdefg");
CaesarCipher test3 = new CaesarCipher(20, "i love csa");
System.out.println("test 1: " + test1.encrypt());
System.out.println("test 2: " + test2.encrypt());
System.out.println("test 3: " + test3.encrypt());
test 1: khoor zruog
test 2: klmnopq
test 3: c fipy wmu
2
15
15
Iteration: 0
Current Velocity: 2, 2