Question

281. 锯齿迭代器

English Version

题目描述

给出两个一维的向量，请你实现一个迭代器，交替返回它们中间的元素。

示例:

输入:
v1 = [1,2]
v2 = [3,4,5,6] 

输出: [1,3,2,4,5,6]

解析: 通过连续调用 _next_ 函数直到 _hasNext_ 函数返回 false，
   _next_ 函数返回值的次序应依次为: [1,3,2,4,5,6]。

拓展：假如给你 k 个一维向量呢？你的代码在这种情况下的扩展性又会如何呢?

拓展声明：
 “锯齿” 顺序对于 k > 2 的情况定义可能会有些歧义。所以，假如你觉得 “锯齿” 这个表述不妥，也可以认为这是一种 “循环”。例如：

输入:
[1,2,3]
[4,5,6,7]
[8,9]

输出: [1,4,8,2,5,9,3,6,7].

解法

方法一

class ZigzagIterator:
  def __init__(self, v1: List[int], v2: List[int]):
    self.cur = 0
    self.size = 2
    self.indexes = [0] * self.size
    self.vectors = [v1, v2]

  def next(self) -> int:
    vector = self.vectors[self.cur]
    index = self.indexes[self.cur]
    res = vector[index]
    self.indexes[self.cur] = index + 1
    self.cur = (self.cur + 1) % self.size
    return res

  def hasNext(self) -> bool:
    start = self.cur
    while self.indexes[self.cur] == len(self.vectors[self.cur]):
      self.cur = (self.cur + 1) % self.size
      if self.cur == start:
        return False
    return True


# Your ZigzagIterator object will be instantiated and called as such:
# i, v = ZigzagIterator(v1, v2), []
# while i.hasNext(): v.append(i.next())

public class ZigzagIterator {
  private int cur;
  private int size;
  private List<Integer> indexes = new ArrayList<>();
  private List<List<Integer>> vectors = new ArrayList<>();

  public ZigzagIterator(List<Integer> v1, List<Integer> v2) {
    cur = 0;
    size = 2;
    indexes.add(0);
    indexes.add(0);
    vectors.add(v1);
    vectors.add(v2);
  }

  public int next() {
    List<Integer> vector = vectors.get(cur);
    int index = indexes.get(cur);
    int res = vector.get(index);
    indexes.set(cur, index + 1);
    cur = (cur + 1) % size;
    return res;
  }

  public boolean hasNext() {
    int start = cur;
    while (indexes.get(cur) == vectors.get(cur).size()) {
      cur = (cur + 1) % size;
      if (start == cur) {
        return false;
      }
    }
    return true;
  }
}

/**
 * Your ZigzagIterator object will be instantiated and called as such:
 * ZigzagIterator i = new ZigzagIterator(v1, v2);
 * while (i.hasNext()) v[f()] = i.next();
 */

struct ZigzagIterator {
  v1: Vec<i32>,
  v2: Vec<i32>,
  /// `false` represents `v1`, `true` represents `v2`
  flag: bool,
}

impl ZigzagIterator {
  fn new(v1: Vec<i32>, v2: Vec<i32>) -> Self {
    Self {
      v1,
      v2,
      // Initially beginning with `v1`
      flag: false,
    }
  }

  fn next(&mut self) -> i32 {
    if !self.flag {
      // v1
      if self.v1.is_empty() && !self.v2.is_empty() {
        self.flag = true;
        let ret = self.v2.remove(0);
        return ret;
      }
      if self.v2.is_empty() {
        let ret = self.v1.remove(0);
        return ret;
      }
      let ret = self.v1.remove(0);
      self.flag = true;
      return ret;
    } else {
      // v2
      if self.v2.is_empty() && !self.v1.is_empty() {
        self.flag = false;
        let ret = self.v1.remove(0);
        return ret;
      }
      if self.v1.is_empty() {
        let ret = self.v2.remove(0);
        return ret;
      }
      let ret = self.v2.remove(0);
      self.flag = false;
      return ret;
    }
  }

  fn has_next(&self) -> bool {
    !self.v1.is_empty() || !self.v2.is_empty()
  }
}