算法:dp+字典树 题目链接Ann and Half-Palindrome   在CF刷字符串题的时候遇到了这题,其实并没有黑题这么难,个人感觉最多是紫题吧(虽然一开始以为是后缀自动机的神仙题).   首先注意到字符串 \(s\) 长度很小( \(1\le|s|\le5000\) ),可以 \(\mathcal O(n^2)\) 地把所有子串求出来,再用Trie树存起来,这样就方便我们dfs求字典序第 \(k\) 小的半回文串.所以问题重心变为怎么快速判断这些子串是否为半回文串.根据半回文串的特…

http://poj.org/problem?id=3974 题目大意: 求最大回文子串长度. ———————————————————— 马拉车板子题. 马拉车大概讲解: 首先在每两个字母之间插入‘#’ id为一个回文串的中点,mx为该串的右端点,p[i]为以i为中点的回文串长度. 假设我们求完了上述的mx和id,枚举i的时候,我们有: if(mx>i)p[i]=min(p[2*id-i],mx-i); (显然i在该回文串中,左右对称可得该式子(如果i对称的点所在的回文串在id的回文串里面那么就…

http://acm.timus.ru/problem.aspx?space=1&num=1297 https://vjudge.net/problem/URAL-1297 给定一个字符串,求最长回文子串. 论文题,摘一下论文的图片,保证一下就看懂了. (由于我摘不下来图片所以用了https://www.cnblogs.com/lidaxin/p/5002878.html的图片,代码也是参考的他) emm要是还没看懂的话稍微解释一下吧. 也就是说,实际上我们是把反串接到正串后面,然后后缀数组高度…

现在看这道题也不难啊,不知道考场上为啥没切~ code: #include <bits/stdc++.h> #define N 5006 #define setIO(s) freopen(s".in","r",stdin) using namespace std; struct trie { int size,tag,ch[2]; }p[N*2500]; char S[N]; int f[N][N],tot; void dfs(int u) { p[u]…

题目: Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases. For example, "A man, a plan, a canal: Panama" is a palindrome. "race a car" is not a palindrome. Note: Have you consider…

Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases. For example,"A man, a plan, a canal: Panama" is a palindrome."race a car" is not a palindrome. Note:Have you consider that th…

9. Palindrome Number Easy Determine whether an integer is a palindrome. An integer is a palindrome when it reads the same backward as forward. Example 1: Input: 121 Output: true Example 2: Input: -121 Output: false Explanation: From left to right, it…

第一周: 经过漫长的时间,终于有时间来写一下结题报告. 地址http://acm.hust.edu.cn/vjudge/contest/view.action?cid=36180#overview A:POJ 1837       Balance      按偏移量DP                                                   题解 B:POJ 1948        Triangular Pastures   按边长DP                …

A. Karen and Morning time limit per test 2 seconds  memory limit per test 512 megabytes input standard input output standard output Karen is getting ready for a new school day! It is currently hh:mm, given in a 24-hour format. As you know, Karen love…

本文出自   http://blog.csdn.net/shuangde800 刘汝佳<算法竞赛入门经典-训练指南>的动态规划部分的习题Beginner  打开 这个专题一共有25题,刷完后对dp的感觉提升了不少. 现把解题报告整理了一下,希望对大家能有帮助. 入门习题 (Exercises: Beginner) UVa11584 Partitioning by Palindromes 入门题目 LA4256 Salesman 入门题目 UVa10534 Wavio Sequence 可以转化…

双指针基础 双指针(Two Pointers)是面对数组.链表结构的一种处理技巧.这里“指针”是泛指,不但包括通常意义上的指针,还包括索引.迭代器等可用于遍历的游标. 同方向指针 设定两个指针.从头往尾(或从尾到头)遍历,我称之为同方向指针,第一个指针用于遍历,第二个指针满足一定条件下移动.例如 LeetCode题目 283. Move Zeroes: // 283. Move Zeroes void moveZeroes(vector<int>& nums) { ; ;j<nu…

前言   [LeetCode 题解]系列传送门:  http://www.cnblogs.com/double-win/category/573499.html   1.题目描述 Determine whether an integer is a palindrome. Do this without extra space. Some hints: Could negative integers be palindromes? (ie, -1) If you are thinking of c…

[题解]Palindrome pairs [Codeforces159D] 传送门:\(Palindrome\) \(pairs\) \([CF159D]\) [题目描述] 给定一个长度为 \(N\) 的字符串 \(S\),求有多少四元组 \((l_1,r_1,l_2,r_2)\) 满足 \(1 \leqslant l_1 \leqslant r_1 \leqslant l_2 \leqslant r_2 \leqslant N\) 且 \(S[l1...r1],\) \([Sl2...r2]\…

题目来源 https://leetcode.com/problems/valid-palindrome/ Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases. For example,"A man, a plan, a canal: Panama" is a palindrome."race a car"…

Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases. For example,"A man, a plan, a canal: Panama" is a palindrome."race a car" is not a palindrome. Note:Have you consider that th…

[题目描述] Implement a function to check if a linked list is a palindrome. 设计一种方式检查一个链表是否为回文链表. [题目链接] www.lintcode.com/en/problem/palindrome-linked-list/ [题目解析] 假设一个链表是回文,那么把链表分割为1-n/2,n/2+1-n两个部分,这两个部分肯定是相同的(把第二部分顺序逆转过来或者逆转第一部分).所以如果我们能把任何一个部分的链表顺序逆转过来…

9. Palindrome Number 题目: Determine whether an integer is a palindrome. Do this without extra space. click to show spoilers. Some hints: Could negative integers be palindromes? (ie, -1) If you are thinking of converting the integer to string, note the…

我现在在做一个叫<leetbook>的开源书项目,把解题思路都同步更新到github上了,需要的同学可以去看看 地址:https://github.com/hk029/leetcode 这个是书的地址:https://hk029.gitbooks.io/leetbook/ 009. Palindrome Number[E] 问题: Determine whether an integer is a palindrome. Do this without extra space. 思路 这里说不…

Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases. For example,"A man, a plan, a canal: Panama" is a palindrome."race a car" is not a palindrome. Note:Have you consider that th…

Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases. For example,"A man, a plan, a canal: Panama" is a palindrome."race a car" is not a palindrome. Note:Have you consider that th…

题目: Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases. For example,"A man, a plan, a canal: Panama" is a palindrome."race a car" is not a palindrome. Note:Have you consider tha…

https://leetcode.com/problems/valid-palindrome/ 题目: Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases. For example,"A man, a plan, a canal: Panama" is a palindrome."race a car"…

题目描写叙述 Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases. For example, "A man, a plan, a canal: Panama" is a palindrome. "race a car" is not a palindrome. Note: Have you consid…

problem: Determine whether an integer is a palindrome. Do this without extra space. click to show spoilers. Some hints: Could negative integers be palindromes? (ie, -1) If you are thinking of converting the integer to string, note the restriction of…

看到Palindrome的题目.首先想到的应该是中心问题,然后从中心出发,思考怎样解决. DP问题通常是从更加小的问题转化到更加大的问题.然后是从地往上 bottom up地计算答案的. 能得出状态转移方程就好办了,本题的状态转移方程是: if (cowID[i] == cow{j]) tbl[id][i] = tbl[id][i+1];//相等的时候无需修改 else tbl[id][i] = min(tbl[!id][i+1] + cost[cowID[i]-'a'], tbl[!id][i…

[题目描述] 给一个非空字符串 s,你最多可以删除一个字符.判断是否可以把它变成回文串. 在线评测地址: https://www.lintcode.com/problem/valid-palindrome-ii/?utm_source=sc-bky-zq [样例] 样例 1: 输入: s = "aba" 输出: true 解释: 原本就是回文串 样例 2: 输入: s = "abca" 输出: true 解释: 删除 'b' 或 'c' 样例 3: 输入: s =…

题目: 判断一个数字是不是回文数字,即最高位与最低位相同,次高位与次低位相同,... 解法: 求出数字的位数,然后依次求商和求余判断是否相等. 代码: class Solution { public: bool isPalindrome(int x) { ) //负数有符号,肯定不是回文数 return false; ; ) //d与x位数相同 d *= ; while(x) { ) //比较最高位和最低位是否相等 return false; x = x % d / ; //去掉最高位和最低位…

题意1:问你一个串有几个不连续子序列(相同字母不同位置视为两个) 题意2:问你一个串有几种不连续子序列(相同字母不同位置视为一个,空串视为一个子序列) 思路1:由容斥可知当两个边界字母相同时 dp[i][j] = dp[i + 1][j] + dp[i][j - 1] - dp[i + 1][j - 1] + dp[i + 1][j - 1] + 1;当两个字母不同时 dp[i][j] = dp[i + 1][j] + dp[i][j - 1] - dp[i + 1][j - 1].然后区间DP…

1.题目描述 2.问题分析 使用两个下标,检测下标对应的字符是否相等,若不相等,则考察子串. 3.代码 bool validPalindrome(string s) { , j = s.size()-; i < j ;i++,j--){ ,j) || isp(s,i,j-); } return true; } bool isp(string s, int l, int r){ for( int i = l, j= r; i < j; i++,j--){ if( s[i] != s[j] ) r…

1.题目描述 2.问题分析 直接用hash table 做就行. 3.代码 int longestPalindrome(string s) { ) ; map<char,int> m; for(auto &c : s) m[c]++; ; ; for(auto p = m.begin(); p != m.end() ; ++p ){ == ) ans += p->second; else{ ans += p->second-; odd++; } } ) ans += ; r…