Huffman和Priority_queue 解決POJ 3253
Description
Farmer John wants to repair a small length of the fence around the pasture. He measures the fence and finds that he needs N (1 ≤ N ≤ 20,000) planks of wood, each having some integer length Li (1 ≤ Li ≤ 50,000) units. He then purchases a single long board just long enough to saw into the N planks (i.e., whose length is the sum of the lengths Li). FJ is ignoring the "kerf", the extra length lost to sawdust when a sawcut is made; you should ignore it, too.
FJ sadly realizes that he doesn't own a saw with which to cut the wood, so he mosies over to Farmer Don's Farm with this long board and politely asks if he may borrow a saw.
Farmer Don, a closet capitalist, doesn't lend FJ a saw but instead offers to charge Farmer John for each of the N-1 cuts in the plank. The charge to cut a piece of wood is exactly equal to its length. Cutting a plank of length 21 costs 21 cents.
Farmer Don then lets Farmer John decide the order and locations to cut the plank. Help Farmer John determine the minimum amount of money he can spend to create the N planks. FJ knows that he can cut the board in various different orders which will result in different charges since the resulting intermediate planks are of different lengths.
Input
Lines 2..N+1: Each line contains a single integer describing the length of a needed plank
Output
Sample Input
3
8
5
8
Sample Output
34
使用優(yōu)先隊(duì)列每次選擇隊(duì)頭的兩個(gè)數(shù)并將其出列,
相加后將結(jié)果放入隊(duì)列中,直到隊(duì)列為空為止.
上面這句話,道出了哈夫曼算法的真諦了。
View Code
#include<iostream> #include<queue> using namespace std; const int Max = 20005; typedef struct node{ long long value; bool operator < (const node &a) const{ return value > a.value; } }node; node tmp; int main() { int n, i; scanf("%d", &n); priority_queue<node> que; for(i = 0; i < n; i ++){ scanf("%d", &tmp.value); que.push(tmp); } long long ans = 0; // 數(shù)值大小的判斷要清楚,別不小心又WA。 while(que.size() > 1){ int a, b; a = que.top().value; que.pop(); b = que.top().value; que.pop(); tmp.value = a + b; que.push(tmp); //將最優(yōu)解再次放入隊(duì)列中,尋找下一個(gè)最優(yōu)解 ans += tmp.value; } cout<<ans<<endl; return 0; }
//經(jīng)過que.push(tmp)之后的排列順序?yàn)?//5
//8
//8
//沒想到就用一個(gè)優(yōu)先隊(duì)列就將哈夫曼樹給實(shí)現(xiàn)了
//這個(gè)從來沒有想到過,牛人呀。
//但是我總覺得,這道題目并沒有將哈夫曼樹的
//作用以發(fā)揮到極點(diǎn)。還會(huì)有后戲的。
還有一個(gè)不用結(jié)構(gòu)體來用優(yōu)先隊(duì)列的方法,但是效率上好像要差一些。
View Code
#include <iostream> #include <queue> using namespace std; int main() { int n; priority_queue<int,vector<int>,greater<int> > qu; //就是這句話了 while(cin>>n) { while(n--) { int x; cin>>x; qu.push(x); } int a=0,b=0; long long res=0; while(qu.size()>1) { a=qu.top(); qu.pop(); b=qu.top(); qu.pop(); res+=a+b; qu.push(a+b) ; } cout<<res<<endl; } return 0; }
posted on 2011-09-25 11:41 More study needed. 閱讀(225) 評(píng)論(0) 收藏 舉報(bào)

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