22题 Flatten List 列表扁平化

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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 Solution {

    // @param nestedList a list of NestedInteger
    // @return a list of integer
    
    public List<Integer> flatten(List<NestedInteger> nestedList) {
        // Write your code here
        List<Integer> result = new ArrayList<Integer>() ;
        for(NestedInteger ele : nestedList ){
            if(ele.isInteger()){
                result.add(ele.getInteger()) ;
            }else{
                result.addAll(flatten(ele.getList())) ;
            }
        }
        return result ;
    }
    
}