LeetCode Pascal's Triangle 杨辉三角 Java

Pascal’s Triangle

Given numRows, generate the first numRows of Pascal’s triangle.

For example, given numRows = 5,

Return

[

[1],

[1,1],

[1,2,1],

[1,3,3,1],

[1,4,6,4,1]

]

这道题比较简单, 杨辉三角, 可以用这一列的元素等于它头顶两元素的和来求.

数学扎实的人会看出, 其实每一列都是

数学里的排列组合

, 第4行, 可以用 C30 = 0 C31=3 C32=3 C33=3 来求

import java.util.ArrayList;
import java.util.List;

public class Par {
    public static void main(String[] args) {
        System.out.println(generate());
        System.out.println(generate());
        System.out.println(generate());
        System.out.println(generate());
        System.out.println(generate());
        System.out.println(generate());

    }

    public static List<List<Integer>> generate(int numRows) {
        List<List<Integer>> result = new ArrayList<List<Integer>>(numRows);
        for (int i = ; i < numRows; i++) {
            List<Integer> thisRow = new ArrayList<Integer>(i);
            thisRow.add();
            int temp = ;
            int row = i;
            for (int j = ; j <= i; j++) {
                temp = temp * row-- / j ;
                thisRow.add(temp);
            }
            result.add(thisRow);
        }
        return result;
    }

}