例题5-7 UVa136 Ugly Numbers(STL:priority_queue)
题意:
看白书
要点:
很简单的priority_queue应用题。之所以写个博客是为了总结一下priority_queue的写法。主要问题是VS中greater不是模板,但OJ中可以AC。
需要特殊排序可以有以下两种写法:
struct node
{
int x, y;
};
struct cmp
{
bool operator()(node a, node b)
{
return a.x > b.x;//注意这里是优先度的意思,如果想从小到大输出要>
}
};
priority_queue<node, vector<node>, cmp > p;
或者:
struct node
{
int x, y;
friend bool operator<(node a, node b)
{
return a.x < b.x;//这里直接重载了<,所以优先度就是从小到大的
}
};
priority_queue<node> pq;
下面是UVa136的代码:
#include<iostream>
#include<set>
#include<queue>
#include<vector>
using namespace std;
typedef long long LL;
const int coff[3] = { 2,3,5 };
struct cmp//升序排列
{
bool operator()(LL &a, LL &b)//仿函数
{
return a > b;
}
};
int main()
{
//priority_queue<LL, vector<LL>, greater<LL> > pq;
priority_queue<LL, vector<LL>, cmp > pq;//VS2015中greater不行但OJ中可以AC
set<LL> s;
pq.push(1);
s.insert(1);
for (int i = 1;; i++)
{
LL x = pq.top();
pq.pop();
if (i == 1500)
{
printf("The 1500'th ugly number is %lld.\n", x);
break;
}
else
{
for (int i = 0; i < 3; i++)
{
LL temp = x*coff[i];
if (!s.count(temp))
{
s.insert(temp);
pq.push(temp);
}
}
}
}
return 0;
}