挑战程序设计竞赛(1.6-p26)

挑战程序设计竞赛

标签 ： acm
参考

P26

1.6 有n根棍子，棍子i的长度为ai，想要从中选出3根棍子组成周长尽可能长的三角形，请输出最大的周长，若无法组成三角形则输出0。

思路：直接三重循环遍历能得到结果，时间复杂度为$O(n^3)$,如果给定的棍子是排好序的，那事情就好办了，若
$n1<n2<n3<n4<...<nk$,选取邻近的三个数即可。显然如果选择为ni,n(i+1),n(i+2)

#define ONLINE_JUDGE#include <iostream>#include <vector>#include <iterator>#include <algorithm>#include <functional>using namespace std;int main(int argc, char *argv[]){#ifndef ONLINE_JUDGE    freopen("in.txt", "r", stdin);    freopen("out.txt", "w", stdout);#endif    int n;    cin >> n;    vector<int> coll;    copy(istream_iterator<int>(cin), istream_iterator<int>(), back_inserter(coll));    sort(coll.begin(), coll.end(), greater<int>());    //copy(coll.begin(), coll.end(), ostream_iterator<int>(cout, " "));    bool found = false;    for (int i = 0; i < n - 2; ++i)    {        if (coll[i] < coll[i + 1] + coll[i + 2])        {            cout << coll[i] + coll[i + 1] + coll[i + 2] << endl;            found = true;            break;        }    }    if (!found)    {        cout << 0 << endl;    }#ifndef ONLINE_JUDGE    fclose(stdin);    fclose(stdout);    system("out.txt");#endif    return 0;}