From cc5ab15011c8d113aa7ea7c39440110e9671866c Mon Sep 17 00:00:00 2001
From: ShusenTang <tangshusen@pku.edu.cn>
Date: Wed, 11 Dec 2019 11:07:25 +0800
Subject: [PATCH] Create 341. Flatten Nested List Iterator.md

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+# [341. Flatten Nested List Iterator](https://leetcode.com/problems/flatten-nested-list-iterator/)
+
+# 思路
+
+这道题让我们将嵌套链表压平。
+
+思路很简单，因为链表的元素可能还是链表，所以是个递归（或者用栈转成非递归），我们先创建一个记录压平后所有元素的全局数组nums，
+然后定义helper递归函数，传入一个`NestedInteger`记为`nest`:
+* 若`nest.isInteger() == True`，即`nest`是个数，将`nest.getInteger()`push进nums即可；
+* 否则，即`nest`是个列表，那么对`nest.getList()`的每个元素递归调用helper。
+
+NestedIterator构造函数里面，我们对nestedList每个元素调用一下`helper`以建立nums，建立好nums后，`hasNext()`和`next()`就好写了。
+
+# C++
+``` C++
+class NestedIterator {
+private:
+    int cur_index, size;
+    vector<int>nums;
+    void helper(NestedInteger &nest){
+        if(nest.isInteger())
+            nums.push_back(nest.getInteger());
+        else{
+            auto &list = nest.getList();
+            for(auto &a: list)
+                helper(a);
+        }     
+    }
+    
+public:
+    NestedIterator(vector<NestedInteger> &nestedList) {
+        cur_index = 0;
+        for(auto & a: nestedList)
+            helper(a);
+        size = nums.size();
+    }
+
+    int next() {
+        return nums[cur_index++];
+    }
+
+    bool hasNext() {
+        return cur_index < size;
+    }
+};
+```