likesky3
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likesky3：
看了数据结构书得知并不是迭代和递归的区别，yb君的写法的效果是 ...
Leetcode - Graph Valid Tree -
likesky3：
迭代和递归的区别吧~
Leetcode - Graph Valid Tree -
qb_2008：
还有一种find写法：int find(int p) { i ...
Leetcode - Graph Valid Tree -
qb_2008：
要看懂这些技巧的代码确实比较困难。我是这么看懂的：1. 明白这 ...
Leetcode - Single Num II -
qb_2008：
public int singleNumber2(int[] ...
Leetcode - Single Num II
文章列表
There are a row of n houses, each house can be painted with one of the k colors. The cost of painting each house with a certain color is different. You have to paint all the houses such that no two adjacent houses have the same color.
The cost of painting each house with a certain color is represent ...
[分析]
将各个正数放入相应下标处，使之满足nums[nums[i] - 1] = nums[i]，则一遍扫描后值在数组长度范围内的都按序排列了，然后二遍扫描遇到第一个打破秩序的位置i,则 i + 1就是第一个缺失的正数。
[ref]
解析清楚的Code Ganker博客：http://blog.csdn.net/linhuanmars/article/details/20884585
简洁的实现：https://leetcode.com/discuss/24013/my-short-c-solution-o-1-space-and-o-n-time
public class Soluti ...
Given a m x n matrix, if an element is 0, set its entire row and column to 0. Do it in place.
[分析]
错误思路：第一遍扫描矩阵，遇到0时将其所在行和列非0元素标记为一个特殊符号。第二遍扫描，将所有特殊符号置0。但因为矩阵元素是整数，找不到不能用整数表示的特殊符号，总有case过不了。
正确的思路是使用两个数组在扫描数组过程中分别存储各行各列是否需要被清零的判断，优化的实现是使用输入矩阵的第一行和第一列进行存储，让matrix[0][0]代表第一行的情况，则还需另一个变量col0存放第一列的状态。第一 ...
[分析]
自己的思路：从外到内一圈圈顺时针旋转90度，坐标映射问题。
Leetcode讨论区有很多有趣巧妙的思路，列举两个点赞率较高思路：
1）上下颠倒，然后转置
/*
* clockwise rotate
* first reverse up to down, then swap the symmetry
* 1 2 3 7 8 9 7 4 1
* 4 5 6 => 4 5 6 => 8 5 2
* 7 8 9 1 2 3 9 6 3
*/
2）转置，然后左右颠倒
若需要逆时针，则分别是：
1）左右颠倒，然后转置
2）转置，然后上下颠 ...
[分析]
此题若不考虑极大值极小值相关的corner case是简单的，如base version，当前leetcode的test case没有包含这些边缘case，因此是可以通过的。下面给出两种实现，base version和做了防溢出处理的robust version，并提供了相应的test case。
遇到整数数组问题，需要特别留意溢出问题，面试时可先写出base version然后再考虑增加放溢出处理，不然后者可能严重干扰主干思路，对我来说，添加上防溢出处理的时间远多于写出base version的时间。
public class MissingRanges {
@T ...
Given an array of n integers where n > 1, nums, return an array output such that output[i] is equal to the product of all the elements of nums except nums[i].
Solve it without division and in O(n).
For example, given [1,2,3,4], return [24,12,8,6].
Follow up:
Could you solve it with constant spa ...
Given an array of n integers nums and a target, find the number of index triplets i, j, k with 0 <= i < j < k < n that satisfy the condition nums[i] + nums[j] + nums[k] < target.
For example, given nums = [-2, 0, 1, 3], and target = 2.
Return 2. Because there are two triplets which s ...
Given an integer n, generate a square matrix filled with elements from 1 to n2 in spiral order.
For example,
Given n = 3,
You should return the following matrix:
[
[ 1, 2, 3 ],
[ 8, 9, 4 ],
[ 7, 6, 5 ]
]
[分析]
实现2参考https://leetcode.com/discuss/14079/my-super-simple-solution-can-used-for-both-spi ...
Given a matrix of m x n elements (m rows, n columns), return all elements of the matrix in spiral order.
For example,
Given the following matrix:
[
[ 1, 2, 3 ],
[ 4, 5, 6 ],
[ 7, 8, 9 ]
]
You should return [1,2,3,6,9,8,7,4,5].
[分析]
思路1：螺旋遍历就是从外到内一圈圈顺时针遍历，记每一圈起始的坐标为xStart, yStart, 每一圈x方向半径为xRad ...
Given an array of integers and an integer k, find out whether there are two distinct indices i and j in the array such that nums[i] = nums[j] and the difference between i and j is at most k.
[分析]
思路1：使用HashSet, HashSet中存最近访问的 k 个元素，从第 k + 1个元素开始遍历检查，若 HashSet中存在同当前访问元素相同的说明 k 邻域内存在重复元素，否则添加当前元素并删除与其 ...
This is a follow up of Shortest Word Distance. The only difference is now you are given the list of words and your method will be called repeatedly many times with different parameters. How would you optimize it?
Design a class which receives a list of words in the constructor, and implements a meth ...
This is a follow up of Shortest Word Distance. The only difference is now word1 could be the same as word2.
Given a list of words and two words word1 and word2, return the shortest distance between these two words in the list.
word1 and word2 may be the same and they represent two individual words ...
Given a list of words and two words word1 and word2, return the shortest distance between these two words in the list.
For example,
Assume that words = ["practice", "makes", "perfect", "coding", "makes"].
Given word1 = “coding”, word2 = “practice”, ...
Given an array of numbers nums, in which exactly two elements appear only once and all the other elements appear exactly twice. Find the two elements that appear only once.
For example:
Given nums = [1, 2, 1, 3, 2, 5], return [3, 5].
Note:
The order of the result is not important. So in the above ...
All DNA is composed of a series of nucleotides abbreviated as A, C, G, and T, for example: "ACGAATTCCG". When studying DNA, it is sometimes useful to identify repeated sequences within the DNA.
Write a function to find all the 10-letter-long sequences (substrings) that occur more than once ...