POJ 1948 Triangular Pastures（二维背包） - ACway的专栏 - 博客频道 - CSDN.NET

POJ 1948 Triangular Pastures（二维背包） - ACway的专栏 - 博客频道 - CSDN.NET

Like everyone, cows enjoy variety. Their current fancy is new shapes for pastures. The old rectangular shapes are out of favor; new geometries are the favorite. 

I. M. Hei, the lead cow pasture architect, is in charge of creating a triangular pasture surrounded by nice white fence rails. She is supplied with N (3 <= N <= 40) fence segments (each of integer length Li (1 <= Li <= 40) and must arrange them into a triangular pasture with the largest grazing area. Ms. Hei must use all the rails to create three sides of non-zero length. 

Help Ms. Hei convince the rest of the herd that plenty of grazing land will be available.Calculate the largest area that may be enclosed with a supplied set of fence segments. 

Input

* Line 1: A single integer N 

* Lines 2..N+1: N lines, each with a single integer representing one fence segment's length. The lengths are not necessarily unique. 

Output

A single line with the integer that is the truncated integer representation of the largest possible enclosed area multiplied by 100. Output -1 if no triangle of positive area may be constructed. 

Sample Input

5  1  1  3  3  4  

Sample Output

692  

Hint

[which is 100x the area of an equilateral triangle with side length 4] 

   题意：

  求n条线段构成的三角形的最大面积*100

  题解

  由于三角形有三个边，并且所有的线段都要用到，于是可以用dp[i][j]表示边长为i,j,sum-i-j的三角形，由于是二维的，j，k边有一个可以取到0，另一个减去a后要大于等于0，最后用海伦公式算面积。

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