You are given a nested list of integers nestedList. Each element is either an integer or a list whose elements may also be integers or other lists. Implement an iterator to flatten it.
Implement the NestedIterator class:
NestedIterator(List<NestedInteger> nestedList) Initializes the iterator with the nested list nestedList.
int next() Returns the next integer in the nested list.
boolean hasNext() Returns true if there are still some integers in the nested list and false otherwise.
Example 1:
Input: nestedList = [[1,1],2,[1,1]]
Output: [1,1,2,1,1]
Explanation: By calling next repeatedly until hasNext returns false, the order of elements returned by next should be: [1,1,2,1,1].
Example 2:
Input: nestedList = [1,[4,[6]]]
Output: [1,4,6]
Explanation: By calling next repeatedly until hasNext returns false, the order of elements returned by next should be: [1,4,6].
Constraints:
1 <= nestedList.length <= 500
The values of the integers in the nested list is in the range [-106, 106].
Solution:
public class NestedIterator implements Iterator<Integer> {
Stack<NestedInteger> stack = new Stack<NestedInteger>();
public NestedIterator(List<NestedInteger> nestedList) {
if(nestedList==null)
return;
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 top = stack.peek();
if(top.isInteger()){
return true;
}else{
stack.pop();
for(int i=top.getList().size()-1; i>=0; i--){
stack.push(top.getList().get(i));
}
}
}
return false;
}
}
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