Integer to Roman

Problem

Given an integer, convert it to a roman numeral.
Input is guaranteed to be within the range from 1 to 3999.

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Idea

定义好radix和symbol很重要

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Solution

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Populating Next Right Pointers in Each Node

Problem

Too long. Check the 传送们:

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Idea

完全binary tree节点数n和层数h的关系

n = 2^(h)-1;     （h从1开始）

先把每一层的最右边的next = NULL设置好，然后遍历每一层，起点是每层最左边的点，遍历每个点，把这个点下面的左孩子和右孩子连起来，然后再遍历一次，把不是同一个parent的两个相邻点连起来

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Solution

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Binary Tree Inorder Traversal

Problem

Given a binary tree, return the inorder traversal of its nodes' values.

For example:

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Idea

Use stack. Push left child to stack ＆nbsp > ＆nbsp push_back(parent->val) to result ＆nbsp > ＆nbsp push right child to stack.

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Solution

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Binary Tree Level Order Traversal II

Problem

Given a binary tree, return the bottom-up level order traversal of its nodes' values. (ie, from left to right, level by level from leaf to root).

For example:

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Idea

做法与binary tree level order traversal 类似。不同的地方是别忘记把结果倒过来.

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Solution

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Binary Tree Preorder Traversal

Problem

Given a binary tree, return the preorder traversal of its nodes' values.

For example:
Given binary tree {1,#,2,3},
  1
   \
    2
   /
  3
return [1,2,3].

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Idea

stack 实现根 左 右。

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Solution

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Best Time to Buy and Sell Stock 3

Problem

Say you have an array for which the ith element is the price of a given stock on day i.
Design an algorithm to find the maximum profit. You may complete at most two transactions.

Note:
You may not engage in multiple transactions at the same time (ie, you must sell the stock before you buy again).

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Idea

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Solution

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Binary Tree Level Order Traversal

Problem

Given a binary tree, return the level order traversal of its nodes' values. (ie, from left to right, level by level).

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Idea

BFS can solve this problem.

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Note

C++ queue

Solution

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