stack 相关

2022-02-20 23:33:17 阅读：148 来源： 互联网

标签：nested list stack next 相关 nestedList public

341. Flatten Nested List Iterator Medium

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.

Your code will be tested with the following pseudocode:

initialize iterator with nestedList
res = []
while iterator.hasNext()
    append iterator.next() to the end of res
return res

If res matches the expected flattened list, then your code will be judged as correct.

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].

/**
 * // 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 empty list if this NestedInteger holds a single integer
 *     public List<NestedInteger> getList();
 * }
 */
public class NestedIterator implements Iterator<Integer> {
    Stack<NestedInteger> stack;
    public NestedIterator(List<NestedInteger> nestedList) {
        stack = new Stack();
        fill(nestedList,stack);
    }
    @Override
    public Integer next() {
        if(!hasNext()) return -1;
        Integer curr = stack.pop().getInteger();
        return curr;
    }
    @Override
    public boolean hasNext() {
        while(!stack.isEmpty() && !stack.peek().isInteger() ) {
            fill(stack.pop().getList(),stack);
        }
        return !stack.isEmpty();
    }
    private void fill(List<NestedInteger> nestedList,Stack<NestedInteger> stack){
        for(int i=nestedList.size()-1;i>=0;i--){
            stack.push(nestedList.get(i));
        }
    }
}

标签：nested,list,stack,next,相关,nestedList,public
来源： https://www.cnblogs.com/cynrjy/p/15917029.html

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stack 相关