How Many Triangles 题目连接: http://acm.hdu.edu.cn/showproblem.php?pid=5784 Description Alice has n points in two-dimensional plane. She wants to know how many different acute triangles they can form. Two triangles are considered different if they differ…

计算几何,极角排序,双指针,二分. 直接找锐角三角形的个数不好找,可以通过反面来求解. 首先,$n$个点最多能组成三角形个数有$C_n^3$个,但是这之中还包括了直角三角形,钝角三角形,平角三角形,我们需要减去这些三角形的个数. 如果在$n$个点中找到了$A$个直角,那么必然有$A$个直角三角形. 同理,如果找到了$B$个钝角,那么必然有$B$个钝角三角形. 同理,如果找到了$C$个平角,那么必然有$C$个平角三角形. 那么答案:$ans=C_n^3-A-B-C$. 接下里的任务就是求解$A$,…

Problem How Many Triangles (HDU 5784) 题目大意 给定平面上的n个点(n<2000),询问可以组成多少个锐角三角形. 解题分析 直接统计锐角三角形较困难,考虑问题的反面,统计直角三角形.钝角三角形.平角三角形(暂时这么叫吧QAQ). 首先枚举三角形的一个端点A,对其他点进行象限为第一关键字,极角为第二关键字排序. 然后使用三个指针,进行O(n)的扫描. 具体做法为用 i 指针指向三角形的第二个端点B.我们可以假想通过平移和旋转,把A点置于平面直角坐标系的原点,…

Peter has a sequence a1,a2,...,ana1,a2,...,an and he define a function on the sequence -- F(a1,a2,...,an)=(f1,f2,...,fn)F(a1,a2,...,an)=(f1,f2,...,fn) , where fifi is the length of the longest increasing subsequence ending with aiai . Peter would lik…

题目链接:http://acm.hdu.edu.cn/showproblem.php?pid=5135 题目大意:给你n条边,选出若干条边,组成若干个三角形,使得面积和最大.输出最大的面积和. 先将边从小到大排序,这样前面的两条边加起来如果不大于第三条边就可以跳出,这是一个存在性条件. dfs(int idx,int now,int cnt,int nowmax)代表我当前处理的是第idx条边,已经加入边集的有cnt条边,当前的边的长度和为now,组成的最大面积和为nowmax. 暴力枚举每个三…

Counting Triangles Problem Description Given an equilateral triangle with n thelength of its side, program to count how many triangles in it. Input The length n (n <= 500) of theequilateral triangle's side, one per line. process to the end of the fil…

http://acm.hdu.edu.cn/showproblem.php?pid=5135 题意:给你N个木棍的长度,然后让你组成三角形,问你组成的三角形的和最大是多少? 思路:先求出可以组成的所有的三角形,然后状压dp就可以.求所有的三角形也可以用状压,也可以三重循环求. #include <cstdio> #include <cstring> #include <cmath> #include <algorithm> #define maxn 1<…

Counting Triangles Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)Total Submission(s): 1882    Accepted Submission(s): 898 Problem Description Given an equilateral triangle with n the length of its side, program to…

转载:from http://blog.csdn.net/qq_28236309/article/details/47818349 基础题:1000.1001.1004.1005.1008.1012.1013.1014.1017.1019.1021.1028.1029. 1032.1037.1040.1048.1056.1058.1061.1070.1076.1089.1090.1091.1092.1093. 1094.1095.1096.1097.1098.1106.1108.1157.116…

传送门:http://acm.hdu.edu.cn/showproblem.php?pid=6300 Triangle Partition Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 132768/132768 K (Java/Others)Total Submission(s): 2964    Accepted Submission(s): 1474Special Judge Problem Description Chia…