341. Flatten Nested List Iterator

341. Flatten Nested List Iterator

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].

/** * // 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(); * * // @returnpublic class NestedIterator implements Iterator { Stack> stk; Iterator tempIter; Integer temp = null; public NestedIterator(List nestedList) { stk = new Stack>(); tempIter = nestedList.iterator(); temp = findNextInt(); } @Override public Integer next() { int res = temp; temp = findNextInt(); return res; } public Integer findNextInt() { while (tempIter.hasNext() || !stk.isEmpty()) { if (tempIter.hasNext()) { NestedInteger i = tempIter.next(); if (i.isInteger()) { return i.getInteger(); } else { stk.push(tempIter); tempIter = i.getList().iterator(); } } else { tempIter = stk.pop(); } } return null; } @Override public boolean hasNext() { return temp != null; }}/** * Your NestedIterator object will be instantiated and called as such: * NestedIterator i = new NestedIterator(nestedList); * while (i.hasNext()) v[f()] = i.next(); */

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