LintCode-22. 平面列表

题目描述

给定一个列表，该列表中的每个要素要么是个列表，要么是整数。将其变成一个只包含整数的简单列表。

注意事项

如果给定的列表中的要素本身也是一个列表，那么它也可以包含列表

样例

给定 [1,2,[1,2]]，返回 [1,2,1,2]。

给定 [4,[3,[2,[1]]]]，返回 [4,3,2,1]。

挑战

请用非递归方法尝试解答这道题。

分析

根据已知的函数一直将列表里的整数取出来就好了。

代码

/**
* // This is the interface that allows for creating nested lists.
* // You should not implement it, or speculate about its implementation
* class NestedInteger {
*   public:
*     // Return true if this NestedInteger holds a single integer,
*     // rather than a nested list.
*     bool isInteger() const;
*
*     // Return the single integer that this NestedInteger holds,
*     // if it holds a single integer
*     // The result is undefined if this NestedInteger holds a nested list
*     int getInteger() const;
*
*     // Return the nested list that this NestedInteger holds,
*     // if it holds a nested list
*     // The result is undefined if this NestedInteger holds a single integer
*     const vector<NestedInteger> &getList() const;
* };
*/
class Solution {
public:
// @param nestedList a list of NestedInteger
// @return a list of integer
vector<int> flatten(vector<NestedInteger> &nestedList) {
// Write your code here
vector<int> result;
for(NestedInteger it : nestedList) {
if(it.isInteger()) {
result.push_back(it.getInteger());
} else {
vector<NestedInteger> nlist = it.getList();
vector<int> ilist = flatten(nlist);
result.insert(result.end(), ilist.begin(), ilist.end());
}
}
return result;
}
};

优化

关于挑战中不用递归的要求，做了以下修改。

/**
* // This is the interface that allows for creating nested lists.
* // You should not implement it, or speculate about its implementation
* class NestedInteger {
*   public:
*     // Return true if this NestedInteger holds a single integer,
*     // rather than a nested list.
*     bool isInteger() const;
*
*     // Return the single integer that this NestedInteger holds,
*     // if it holds a single integer
*     // The result is undefined if this NestedInteger holds a nested list
*     int getInteger() const;
*
*     // Return the nested list that this NestedInteger holds,
*     // if it holds a nested list
*     // The result is undefined if this NestedInteger holds a single integer
*     const vector<NestedInteger> &getList() const;
* };
*/
class Solution {
public:
// @param nestedList a list of NestedInteger
// @return a list of integer
vector<int> flatten(vector<NestedInteger> &nestedList) {
// Write your code here
vector<int> result;
vector<NestedInteger> nlist = nestedList;
int flag = 1;
while(flag) {
flag = 0;
vector<NestedInteger> temp;
for(NestedInteger it : nlist) {
if(it.isInteger()) {
temp.push_back(it);
} else {
vector<NestedInteger> list = it.getList();
temp.insert(temp.end(), list.begin(), list.end());
flag = 1;
}
}
nlist = temp;
}
for(NestedInteger it : nlist) {
result.push_back(it.getInteger());
}
return result;
}
};

总结

vectorAPI文档