打印杨辉三角

今天面试遇到的一道老题目，打印出杨辉三角，面试的时候我的解法没有让自己满意，回来后又改了些版本，我也看了下网上的方法，这里我提供一个不一样的思路，以面向对象的思想去解决这个问题，我把整个杨辉三角作为对象YangHuiTriangle，每一行的内容作为对象YangHuiRow，Triangle由Row组成，有多少行的内容就有多少个YangHuiRow对象，这样思路比较清晰，我比较满意我的这个解决方法，拿出来和大家分享一下。

YangHuiRow我是这么设计的，由于杨辉三角的每一行都是左右对称的，所以可以用两个集合对象去存储左右两边的数字，而打印的时候总是从左至右，那么左边前进先出应该用队列，右边先进后出则用栈去解决，而又因为有奇数行和偶数行的关系，所以我添加了一个整型变量用来存储奇数行的中间数字，整体的一个思路就是这样子的。

下面是YangHuiRow的代码：

public class YangHuiRow {
    private int rowIndex;
    private Queue<Integer> left = new LinkedList<Integer>();
    private int middle;
    private Stack<Integer> right = new Stack<Integer>();

    public void insert(int num) {
        left.offer(num);
        right.push(num);
    }

    public YangHuiRow(int rowIndex) {
        this.rowIndex = rowIndex;
        if (rowIndex == 1) {
            middle = 1;
        } else {
            insert(1);
        }
    }

    public void setAboveRow(YangHuiRow aboveRow) throws Throwable {
        rowIndex = aboveRow.getRowIndex() + 1;
        clear();
        int index = 0;
        int[] nums = aboveRow.getNums();
        if (aboveRow.isOdd() && !isOdd()) {
            for (int i = 0; i < aboveRow.size() / 2; i++) {
                insert(nums[index] + nums[++index]);
            }
        } else if (!aboveRow.isOdd() && isOdd()) {
            for (int i = 1; i < aboveRow.size() / 2; i++) {
                insert(nums[index] + nums[++index]);
            }
            middle = (nums[index] + nums[++index]);
        } else {
            throw new Throwable("error");
        }
    }

    public boolean isOdd() {
        return rowIndex % 2 == 1;
    }

    @SuppressWarnings("unchecked")
    public int[] getNums() {
        int[] arr = new int[size()];
        int i = 0;
        Queue<Integer> l = (Queue<Integer>) ((LinkedList<Integer>) left)
                .clone();
        Stack<Integer> r = (Stack<Integer>) right.clone();
        while (l.size() > 0) {
            arr[i++] = l.poll();
        }
        if (isOdd()) {
            arr[i++] = middle;
        }
        while (r.size() > 0) {
            arr[i++] = r.pop();
        }
        return arr;
    }

    public int size() {
        return (this.isOdd() ? 1 : 0) + left.size() + right.size();
    }

    public int getRowIndex() {
        return rowIndex;
    }

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        for (Integer i : getNums()) {
            sb.append(i + " ");
        }
        return sb.toString();
    }

    public void clear() {
        left.clear();
        right.clear();
        if (rowIndex == 1) {
            middle = 1;
        } else {
            insert(1);
        }
    }
}

 

 下面是YangHuiTriangle的代码：

public class YangHuiTriangle {
    private Stack<YangHuiRow> rows = new Stack<YangHuiRow>();

    public YangHuiTriangle(int rowCount) throws Throwable {
        if (rowCount < 3) {
            throw new Throwable("row count must be bigger than 2");
        }
        rows.add(new YangHuiRow(1));
        rows.add(new YangHuiRow(2));
        for (int i = 2; i < rowCount; i++) {
            YangHuiRow newRow = new YangHuiRow(rows.size() + 1);
            newRow.setAboveRow(rows.peek());
            rows.push(newRow);
        }
    }

    public void printRows() {
        for (YangHuiRow r : rows) {
            for (int i = 0; i < rows.size() - r.getRowIndex(); i++)
                System.out.print("  ");
            System.out.println(r.toString());
        }
    }

    public static void main(String[] args) {
        try {
            new YangHuiTriangle(12).printRows();
        } catch (Throwable e) {
            e.printStackTrace();
        }
    }
}

 

欢迎批评指正。