【python】Leetcode每日一题-扁平化嵌套列表迭代器

【python】Leetcode每日一题-扁平化嵌套列表迭代器

【题目描述】

给你一个嵌套的整型列表。请你设计一个迭代器，使其能够遍历这个整型列表中的所有整数。

列表中的每一项或者为一个整数，或者是另一个列表。其中列表的元素也可能是整数或是其他列表。

示例1：

输入: [[1,1],2,[1,1]]
输出: [1,1,2,1,1]
解释: 通过重复调用 next 直到 hasNext 返回 false，next 返回的元素的顺序应该是: [1,1,2,1,1]。

示例2：

输入: [1,[4,[6]]]
输出: [1,4,6]
解释: 通过重复调用 next 直到 hasNext 返回 false，next 返回的元素的顺序应该是: [1,4,6]。

---

【分析】

• AC代码：

  # """
  # This is the interface that allows for creating nested lists.
  # You should not implement it, or speculate about its implementation
  # """
  #class NestedInteger:
  #    def isInteger(self) -> bool:
  #        """
  #        @return True if this NestedInteger holds a single integer, rather than a nested list.
  #        """
  #
  #    def getInteger(self) -> int:
  #        """
  #        @return the single integer that this NestedInteger holds, if it holds a single integer
  #        Return None if this NestedInteger holds a nested list
  #        """
  #
  #    def getList(self) -> [NestedInteger]:
  #        """
  #        @return the nested list that this NestedInteger holds, if it holds a nested list
  #        Return None if this NestedInteger holds a single integer
  #        """
  global nested
  nested = []
  class NestedIterator:
      def __init__(self, nestedList):
          for x in nestedList:
              if x.isInteger():
                  nested.append(x.getInteger())
              else:
                  NestedIterator(x.getList())
  
      def next(self) -> int:
          return nested.pop(0)
  
      def hasNext(self) -> bool:
          if(len(nested) == 0):
              return False
          return True
  

• 有兄弟是用正则表达式直接写的

• 官方：

  • dfs

  • 栈

    public class NestedIterator implements Iterator<Integer> {
    
        private Stack<NestedInteger> stack;
        public NestedIterator(List<NestedInteger> nestedList) {
    
            stack = new Stack<>();
            for (int i=nestedList.size()-1;i>=0;i--) {
    
                stack.push(nestedList.get(i));
            }
        }
    
        @Override
        public Integer next() {
    
            NestedInteger temp = stack.pop();
            return temp.getInteger();
        }
    
        @Override
        public boolean hasNext() {
    
            while (!stack.isEmpty()) {
    
                NestedInteger temp = stack.peek();
                if (temp.isInteger()) return true;
    
                stack.pop();
                for (int i=temp.getList().size()-1;i>=0;i--) {
    
                    stack.push(temp.getList().get(i));
                }
            }
            return false;
        }
    }