杨辉三角

给定一个非负整数numRows，生成杨辉三角的前numRows行。

在杨辉三角中，每个数是它的左上方和右上方的数的和。

public List<List<Integer>> generate(int numRows){
    List<List<Integer>> ret = new ArrayList<>();
    List<Integer> row = new ArrayList<>();
    row.add(1);
    ret.add(row);
    for (int i = 0; i < numRows; i++) {
        List<Integer> curRow = new ArrayList<>();
        curRow.add(1);
        List<Integer> prevRow = ret.get(i-1);
        for (int j = 0; j < i; j++) {
            int x = prevRow.get(j)+prevRow.get(j-1);
            curRow.add(x);
        }
        curRow.add(1);
        ret.add(curRow);
    }
    return ret;
} 

洗牌算法

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

public class CardList {
    private static final String[] SUITS = {"♦","❤","♠","♣"};
    public static List<Card> buyCards(){
        List<Card> list = new ArrayList<>();
        for (int i = 0; i < SUITS.length; i++) {
            for (int j = 0; j <= 13; j++) {
                Card card = new Card(SUITS[i],j);
                list.add(card);
            }
        }
        return list;
    }

    public static void shuffle(List<Card> list){
        Random random = new Random();
        for (int i = list.size()-1; i > 0; i++) {
            int index = random.nextInt(i);
            swap(list,i,index);
        }
    }

    private static void swap(List<Card> list,int i,int j){
        Card tmp = list.get(i);
        list.set(i,list.get(i));
        list.set(j,tmp);
    }

    public static void main(String[] args) {
        List<Card> list = buyCards();
        System.out.println(list);

        shuffle(list);
        System.out.println(list);

        List<List<Card>> hand = new ArrayList<>();
        List<Card> hand1 = new ArrayList<>();
        List<Card> hand2 = new ArrayList<>();
        List<Card> hand3 = new ArrayList<>();

        hand.add(hand1);
        hand.add(hand2);
        hand.add(hand3);

        for (int i = 0; i < 5; i++) {
            for (int j = 0; j < 3; j++) {
                Card card = list.remove(0);
                hand.get(j).add(card);
            }
        }
    }
}

public class Card {
    private String suit;
    private int rank;

    public Card(String suit, int rank) {
        this.suit = suit;
        this.rank = rank;
    }

    @Override
    public String toString() {
        return "Card{" +
                "suit='" + suit + '\'' +
                ", rank=" + rank +
                '}';
    }

    public String getSuit() {
        return suit;
    }

    public void setSuit(String suit) {
        this.suit = suit;
    }

    public int getRank() {
        return rank;
    }

    public void setRank(int rank) {
        this.rank = rank;
    }
}