Leetcode Flatten Nested List Iterator (Java)
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 Solution:
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/** * // 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<Iterator<NestedInteger>> s; NestedInteger current; public NestedIterator(List<NestedInteger> nestedList) { s = new Stack<>(); s.push(nestedList.iterator()); } @Override public Integer next() { return current.getInteger(); } @Override public boolean hasNext() { while (!s.empty()) { if(s.peek().hasNext()) { NestedInteger it = s.peek().next(); if(!it.isInteger()) { s.push(it.getList().iterator()); } if(it.isInteger()){ current = it; return true; } } else{ s.pop(); } } return false; } } /** * Your NestedIterator object will be instantiated and called as such: * NestedIterator i = new NestedIterator(nestedList); * while (i.hasNext()) v[f()] = i.next(); |
