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原创蓄水池算法382. Linked List Random Node

碰到一个用到了蓄水池算法的题目：http://blog.jobbole.com/42550//** * Definition for singly-linked list. * public class ListNode { * int val; * ListNode next; * ListNode(int x) { val = x;

2017-07-05 02:41:44 392

原创 [leetCode刷题笔记]373. Find K Pairs with Smallest Sums

public class Solution { public List kSmallestPairs(int[] nums1, int[] nums2, int k) { PriorityQueue queue = new PriorityQueuea[0]+a[1]-b[0]-b[1]); List res = new ArrayList<>();

2017-06-27 12:38:43 407

原创 [leetCode刷题笔记]113. Path Sum II

/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */public class Solution {

2017-06-25 23:46:02 366

原创 [leetCode刷题笔记]47. Permutations II

思路是用一个Boolean array来保存每个元素用过的记录，如果用过，则跳过。处理重复数的时候，先sort，然后如果前一个元素等于后一个元素而且前一个元素已经用过，则跳过后一个元素public class Solution { public List> permuteUnique(int[] nums) { List res = new ArrayLi

2017-06-23 08:23:44 396

原创 [leetCode刷题笔记]260. Single Number III

public class Solution { public int[] singleNumber(int[] nums) { int xor = 0; for (int num : nums) { xor ^= num; } xor &= -xor;

2017-06-22 10:13:15 348

原创 [leetCode刷题笔记]385. Mini Parser

/** * // This is the interface that allows for creating nested lists. * // You should not implement it, or speculate about its implementation * public interface NestedInteger { * // Constructo

2017-06-20 10:17:05 348

原创 [leetCode刷题笔记]112. Path Sum

要是到eft才算。。。。中间的不算的。。。/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } *

2017-06-19 01:34:01 282

原创 [leetCode刷题笔记]347. Top K Frequent Elements

public class Solution { public List topKFrequent(int[] nums, int k) { // frequency array List[] freList = new List[nums.length + 1]; // key: value in nums[] value: frequenc

2017-06-17 12:17:57 312

原创 [leetCode刷题笔记]598. Range Addition II

无聊的奇葩题目。。。public class Solution { public int maxCount(int m, int n, int[][] ops) { if (ops == null || ops.length == 0) return m * n; int col = Integer.MAX_VALUE;

2017-06-17 11:33:29 330

原创 [leetCode刷题笔记]599. Minimum Index Sum of Two Lists

public class Solution { public String[] findRestaurant(String[] list1, String[] list2) { int i = 0; i = 0; Map map2 = new HashMap(); for (String ele : list2 ) {

2017-06-12 02:12:23 469

原创 [leetCode刷题笔记]371. Sum of Two Integers

对bit运算实在不了解"&" AND operation, for example, 2 (0010) & 7 (0111) => 2 (0010)"^" XOR operation, for example, 2 (0010) ^ 7 (0111) => 5 (0101)"~" NOT operation, for example, ~2(0010) => -3 (1101)

2017-06-11 23:53:32 266

原创 [leetCode刷题笔记]520. Detect Capital

public class Solution { public boolean detectCapitalUse(String word) { int count = 0; for(char c: word.toCharArray()) if('Z' - c >= 0) count++; return (

2017-06-11 22:15:45 318

原创 [leetCode刷题笔记]606. Construct String from Binary Tree

奇葩的规则，左子树的规则必须打。/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */public cl

2017-06-09 10:13:25 842

原创 [leetCode刷题笔记]575. Distribute Candies

public class Solution { public int distributeCandies(int[] candies) { Arrays.sort(candies); int len = candies.length; int cur = candies[0]; int di

2017-06-09 09:47:12 382

原创 [leetCode刷题笔记]500. Keyboard Row

public class Solution { public String[] findWords(String[] words) { List sl = new ArrayList(); Map map = new HashMap<>(); String[] key = {"QWERTYUIOP", "ASDFGHJKL", "ZXCV

2017-06-08 10:03:50 331

原创 [leetCode刷题笔记]566. Reshape the Matrix

public class Solution { public int[][] matrixReshape(int[][] nums, int r, int c) { if (nums == null || nums.length == 0 || r * c != nums.length * nums[0].length) return nums; int[]

2017-06-06 11:24:40 304

原创 [leetCode刷题笔记]561. Array Partition I

public class Solution { public int arrayPairSum(int[] nums) { Arrays.sort(nums); int result = 0; for (int i = 0; i < nums.length; i+=2) { result += nums[i];

2017-06-05 08:09:57 402

原创 [leetCode刷题笔记]199. Binary Tree Right Side View

这道题不难，但是要掌握技巧。用recursion来。递归时记下树的深度，当深度等于list的大小时候加入到list里面，并且优先遍历右子树。/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode righ

2017-06-05 07:33:50 339

原创 [leetCode刷题笔记]450. Delete Node in a BST

如果碰到要删除node有两个子node，那么找出右子树的最小值，在赋给node，然后删去最小值原来的那个node/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNod

2017-06-04 10:11:55 337

原创 [leetCode刷题笔记]409. Longest Palindrome

第一种解法： HashSet.将String中的char一个个放入Set中，先检查有没有，如果有的话删除，没有的话加入。public class Solution { public int longestPalindrome(String s) { if (s == null || s.length() == 0) { return 0;

2017-06-04 07:33:46 562

原创 Spring MVC中的session解决方案

之前用PHP做小组项目中用到了session value。在PHP中session value的处理很简单而直接。现在用Spring MVC写项目发现网上的关于Spring mvc 的Session教程写的都不太清楚。所以参考stackoverflow：https://stackoverflow.com/questions/18791645/how-to-use-session-attribu

2017-05-23 01:49:50 600

原创 [leetCode刷题笔记]49. Group Anagrams

将String进行排序，再做成key插入map中，map的value是listpublic class Solution { public List> groupAnagrams(String[] strs) { if (strs == null || strs.length == 0) return new ArrayList>(); Map> str

2017-05-19 06:58:33 289

转载 [SSM]改用SpringMVC

之前Struts2弄了半天，结果别人说Struts2过时了。。。。我是个紧跟时代潮流的人，那就改用SpringMVC吧，先上个网址：http://www.cnblogs.com/bigdataZJ/p/springmvc1.html

2017-05-17 03:36:58 422

原创 [leetCode刷题笔记]300. Longest Increasing Subsequence

DP解决，用dp[len]表示遍历到的最大值，新的值如果大于这个值len++否则替换dp中的一个len不变public class Solution { public int lengthOfLIS(int[] nums) { //use dp[len] to store the largest val. int[] dp = new int[nu

2017-04-28 08:00:19 321

原创 [leetCode刷题笔记]129. Sum Root to Leaf Numbers

public class Solution { public int sumNumbers(TreeNode root) { return helper(root, 0); } private int helper (TreeNode root, int s) { if (root == null) return 0; if (

2017-04-27 11:38:28 268

原创 [leetCode刷题笔记]525. Contiguous Array

用类似动态规划的思路来解决。用HashMap是因为HashMap查找key更快。public class Solution { public int findMaxLength(int[] nums) { // change 0 to -1 for (int i = 0; i < nums.length; i++) { if

2017-04-27 10:34:47 537

原创 [leetCode刷题笔记]284. Peeking Iterator

// Java Iterator interface reference:// https://docs.oracle.com/javase/8/docs/api/java/util/Iterator.htmlclass PeekingIterator implements Iterator { private Iterator ite; private Integer val

2017-04-26 09:43:07 283

原创 [leetCode刷题笔记]494. Target Sum

用递归做，但是比较慢。网上有用动态规划做的http://blog.youkuaiyun.com/hit0803107/article/details/54894227public class Solution { int res = 0; public int findTargetSumWays(int[] nums, int S) { if (nums == nu

2017-04-26 04:59:17 694

原创 [leetCode刷题笔记]22. Generate Parentheses

还是backtrack 一开始一对一对的加括号结果出错了，因为一对括号只能包第一个。还是两个括号分开加。用left和right表示左右括号的数量。public class Solution { public List generateParenthesis(int n) { List res= new ArrayList(); helper(res,

2017-04-25 07:56:56 447

原创 [leetCode刷题笔记]173. Binary Search Tree Iterator

用stack来存储node，先存储最左边的node，再往右移动public class BSTIterator { Stack stack = new Stack(); public BSTIterator(TreeNode root) { pushLeft(root); } /** @return whether we have a nex

2017-04-24 22:36:46 321

原创 [leetCode刷题笔记]46. Permutations

还是用backtrack呀public class Solution { public List> permute(int[] nums) { List> res = new ArrayList>(); helper(res, new ArrayList(), nums); return res; } private vo

2017-04-24 08:37:00 324

原创 [leetCode刷题笔记]341. Flatten Nested List Iterator

思路是这样的：做一个stack，然后在constructor方法中将nestedList中所有元素都添加到这个stack中（最后的元素在最底下）。hasNext方法中，如果stack空了，返回false，否则，先看栈顶元素是否为int，若不为int则getlist再将所有元素压入栈中。如果是int则退出循环public class NestedIterator implements Itera

2017-04-24 05:30:12 508

原创 [leetCode刷题笔记]516. Longest Palindromic Subsequence

动态规划解决问题，dp[][]存放string（i，j）之间palim长度。public class Solution { public int longestPalindromeSubseq(String s) { int[][] dp = new int[s.length()][s.length()]; for (int i = s

2017-04-23 02:35:03 299

原创 [leetCode刷题笔记]491. Increasing Subsequences

这道题用hashset存放list，这样就不会出现重复的情况。如果array里面任何数都不相同，那么不用Set应该也可以public class Solution { public List> findSubsequences(int[] nums) { // using hash set to remove duplicate element Set>

2017-04-22 23:09:17 304

原创 [leetCode刷题笔记]77. Combinations

使用backtrack的方法。对过程进行递归。public class Solution { public List> combine(int n, int k) { List> combs = new ArrayList>(); combine(combs, new ArrayList(), 1, n, k); return combs

2017-04-22 02:57:31 347

原创 [leetCode刷题笔记]504. Base 7

public class Solution { public String convertToBase7(int num) { if (num < 0) { return "-" + convertToBase7(-num); } if (num < 7) { return num + "";

2017-04-21 23:13:13 421

原创 [leetCode刷题笔记]100. Same Tree

递归很简单public class Solution { public boolean isSameTree(TreeNode p, TreeNode q) { if (p != null && q != null) { if (p.val != q.val) return false; else {

2017-04-21 22:39:11 372

原创 [leetCode刷题笔记]503. Next Greater Element II

用一个stack来存储之前的index要遍历两遍array因为存在循环。public class Solution { public int[] nextGreaterElements(int[] nums) { int n = nums.length; int[] res = new int[n]; Arrays.fill(res,

2017-04-21 11:10:34 450

原创 [leetCode刷题笔记]475. Heaters

这道题读题读了半天，大致意思是。给两个数组，第一个数组表示房间的位置，第二个表示加热器的位置，然后想通过设置加热器覆盖的半径来让所有屋子都被加热器覆盖。第一种方法就是找到每个屋子毗邻的加热器，然后再得到所需要最小半径。public class Solution { public int findRadius(int[] houses, int[] heaters) {

2017-04-21 00:03:21 1358

原创 [leetCode刷题笔记]515. Find Largest Value in Each Tree Row

515. Find Largest Value in Each Tree Row使用递归，通过一个数d记录所处树的深度。还有通过比较d和list的长度来确定是添加一个新值，还是比较旧值与新值的大小。注意List的引用一直不变public class Solution { public List largestValues(TreeNode root) { Lis

2017-04-20 09:02:04 532

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