[MeetCoder] Crossing Bridge

Crossing Bridge

Description

N people wish to cross a bridge at night. It’s so dark around there that they have to cross the bridge under the help of a little lamp. Only one little lamp is available (Oh, Men...) and they have to have the little lamp walking with them. The bridge is of a width such that a maximum of 2 people may cross at a time.

Each person walks at his/her fixed speed. If two people cross the bridge together, they must walk at the pace of the slower one. How fast can you get all N people over the bridge?

Input

The input should be a list of N positive integers, where N is less than or equal to 1,000. And each integer of the list should be less than or equal to 100.

Output

The output should be the minimum time that all the people can cross the bridge.

 

Sample Input

1 2

Sample Output

2

HINT

 Greedy

 

过桥问题！主要参考：http://blog.csdn.net/morewindows/article/details/7481851

 1 class Solution {
 2 private:
 3     int _bridge(vector<int> &v, int n) {
 4         if (n == 0) return 0;
 5         if (n == 1) return v[0];
 6         if (n == 2) return v[1];
 7         if (n == 3) return v[0] + v[1] + v[2];
 8         int res = 0;
 9         int a = v[0], b = v[1], x = v[n-2], y = v[n-1];
10         if (2 * b > a + x) res += 2 * a + x + y;
11         else res += a + 2 * b + y;
12         return res + _bridge(v, n - 2);
13     }
14 public:
15     int bridge(vector<int> &v) {
16         sort(v.begin(), v.end());
17         return _bridge(v, v.size());
18     }
19 };
20 /**************************************************************
21     Problem: 45
22     User: easonliu
23     Language: C++
24     Result: Accepted
25     Time:1 ms
26     Memory:2708 kb
27 ****************************************************************/