341. Flatten Nested List Iterator

云计算 waitig 353℃ 百度已收录 0评论

Given a nested list of integers, implement an iterator to flatten it.

Each element is either an integer, or a list — whose elements may also be integers or other lists.

Example 1:
Given the list [[1,1],2,[1,1]],

By calling next repeatedly until hasNext returns false, the order of elements returned by next should be: [1,1,2,1,1].

Example 2:
Given the list [1,[4,[6]]],

By calling next repeatedly until hasNext returns false, the order of elements returned by next should be: [1,4,6].

java

/**
 * // This is the interface that allows for creating nested lists.
 * // You should not implement it, or speculate about its implementation
 * public interface NestedInteger {
 *
 *     // @return true if this NestedInteger holds a single integer, rather than a nested list.
 *     public boolean isInteger();
 *
 *     // @return the single integer that this NestedInteger holds, if it holds a single integer
 *     // Return null if this NestedInteger holds a nested list
 *     public Integer getInteger();
 *
 *     // @return the nested list that this NestedInteger holds, if it holds a nested list
 *     // Return null if this NestedInteger holds a single integer
 *     public List<NestedInteger> getList();
 * }
 */
public class NestedIterator implements Iterator<Integer> {
    
    Stack<NestedInteger> stack = null;
    public NestedIterator(List<NestedInteger> nestedList) {
        stack = new Stack<NestedInteger>();
        for (int i = nestedList.size() - 1; i >= 0; i--) {
            stack.push(nestedList.get(i));
        }
    }
    
    @Override
    public Integer next() {
        return stack.pop().getInteger();
    }

    @Override
    public boolean hasNext() {
        while (!stack.isEmpty()) {
            NestedInteger curr = stack.peek();
            if (curr.isInteger()) {
                return true;
            }
            stack.pop();
            for(int i = curr.getList().size() - 1; i >= 0; i--) {
                stack.push(curr.getList().get(i));
            }
        }
        return false;
    }
}

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

python

# """
# This is the interface that allows for creating nested lists.
# You should not implement it, or speculate about its implementation
# """
#class NestedInteger(object):
#    def isInteger(self):
#        """
#        @return {boolean} True if this NestedInteger holds a single integer,
#        rather than a nested list.
#        """
#
#    def getInteger(self):
#        """
#        @return {int} 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):
#        """
#        @return {NestedInteger[]} the nested list that this NestedInteger holds,
#        if it holds a nested list
#        Return None if this NestedInteger holds a single integer
#        """

class NestedIterator(object):
    
    def __init__(self, nestedList):
        # Initialize your data structure here.
        self.st = nestedList[::-1]
        
    # @return {int} the next element in the iteration
    def next(self):
        # Write your code here
        return self.st.pop().getInteger()
        
    # @return {boolean} true if the iteration has more element or false
    def hasNext(self):
        # Write your code here
        while len(self.st) != 0:
            if self.st[-1].isInteger():
                return True
            curr = self.st.pop()
            self.st = self.st + curr.getList()[::-1]
        return False

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


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