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96. Unique Binary Search Trees Given n, how many structurally unique BST's (binary search trees) that store values 1...n? For example, Given n = 3, th 阅读全文
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530. Minimum Absolute Difference in BST Given a binary search tree with non-negative values, find the minimum absolute difference between values of an 阅读全文
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520. Detect Capital Given a word, you need to judge whether the usage of capitals in it is right or not. We define the usage of capitals in a word to 阅读全文
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递归方法： 非递归：要借助栈，可以利用C++ STL中的stack。首先将根节点压栈，然后压入栈顶元素的左节点直到叶子节点，然后访问叶子节点后压入该节点的右子节点。 阅读全文
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leetcode 105题，由树的前序序列和中序序列构建树结构。详细解答参考《剑指offer》page56. 先序遍历结果的第一个节点为根节点，在中序遍历结果中找到根节点的位置。然后就可以将问题拆分，递归求解。 阅读全文
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437. Path Sum III You are given a binary tree in which each node contains an integer value. Find the number of paths that sum to a given value. The pa 阅读全文
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500. Keyboard Row Given a List of words, return the words that can be typed using letters of alphabet on only one row's of American keyboard like the 阅读全文
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504. Base 7 Given an integer, return its base 7 string representation. Example 1: Input: 100 Output: "202" Example 2: Input: -7 Output: "-10" Note: Th 阅读全文
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28. Implement strStr() Implement strStr(). Returns the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack. 思 阅读全文
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459. Repeated Substring Pattern Given a non-empty string check if it can be constructed by taking a substring of it and appending multiple copies of t 阅读全文
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70. Climbing Stairs You are climbing a stair case. It takes n steps to reach to the top. Each time you can either climb 1 or 2 steps. In how many dist 阅读全文
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53. Maximum Subarray Find the contiguous subarray within an array (containing at least one number) which has the largest sum. For example, given the a 阅读全文
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326. Power of Three Given an integer, write a function to determine if it is a power of three. Follow up: Could you do it without using any loop / rec 阅读全文
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Write an algorithm to determine if a number is "happy". A happy number is a number defined by the following process: Starting with any positive intege 阅读全文
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405. Convert a Number to Hexadecimal Given an integer, write an algorithm to convert it to hexadecimal. For negative integer, two’s complement method 阅读全文
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415. Add Strings Given two non-negative integers num1 and num2 represented as string, return the sum of num1 and num2. Note: 思路：控制num1的长度不小于num2的长度，在n 阅读全文
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108. Convert Sorted Array to Binary Search Tree 思路：利用一个有序数组构建一个平衡二叉排序树。直接递归构建，取中间的元素为根节点，然后分别构建左子树和右子树。 阅读全文
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501. Find Mode in Binary Search Tree Given a binary search tree (BST) with duplicates, find all the mode(s) (the most frequently occurred element) in 阅读全文
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Given an array containing n distinct numbers taken from 0, 1, 2, ..., n, find the one that is missing from the array. For example, Given nums = [0, 1, 阅读全文
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Given n points in the plane that are all pairwise distinct, a "boomerang" is a tuple of points (i, j, k) such that the distance between iand j equals 阅读全文