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Arrays_PascalsTriangle.java
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Arrays_PascalsTriangle.java
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import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.List;
// https://leetcode.com/problems/pascals-triangle/
// https://practice.geeksforgeeks.org/problems/pascal-triangle0652/1
// https://www.youtube.com/watch?v=6FLvhQjZqvM (This explains all the 3 approaches)
// https://www.youtube.com/watch?v=7pOzP9m_bX8&ab_channel=TerribleWhiteboard
public class Arrays_PascalsTriangle {
private static List<List<Integer>> generatePascalsTriangle(int numRows) {
List<List<Integer>> pascalTriangle = new ArrayList<>();
if (numRows == 0) return pascalTriangle;
pascalTriangle.add(new ArrayList<>());
pascalTriangle.get(0).add(1);
for (int rowNum = 1; rowNum < numRows; rowNum++) {
List<Integer> currRow = new ArrayList<>();
List<Integer> prevRow = pascalTriangle.get(rowNum - 1);
currRow.add(1);
for (int i = 0; i < prevRow.size() - 1; i++) {
/* we take two each number and it's next number of previous rows and add them to get the current number */
int numA = prevRow.get(i);
int numB = prevRow.get(i + 1);
currRow.add(numA + numB);
}
currRow.add(1);
pascalTriangle.add(currRow);
}
return pascalTriangle;
}
public static void main(String[] args) throws IOException {
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
int t = Integer.parseInt(br.readLine().trim());
while (t-- > 0) {
int numRows = Integer.parseInt(br.readLine().trim());
List<List<Integer>> output = generatePascalsTriangle(numRows);
print(output);
}
}
private static void print(List<List<Integer>> output) {
StringBuilder sb = new StringBuilder();
for (int i = 0; i < output.size(); i++) {
sb.append("[ ");
for (int j = 0; j < output.get(i).size(); j++) {
sb.append(output.get(i).get(j)).append(" ");
}
sb.append("]").append("\n");
}
System.out.println(sb);
sb.setLength(0);
}
}