USACO算法系列二十六——fence6

    题目：http://www.nocow.cn/index.php/Translate:USACO/fence6

    找周长最小的多边形。使用的还是深度遍历，剪枝的方法。

    #include<iostream>#include <fstream>#define ESIZE 8#define SIZE 101#define LARGENUMBER 0X7FFFFFFFusing namespace std;struct Edge{int s; //标号int ls; //边的长度int n1s; //端点一的边数int n1array[ESIZE];int n2s; //端点二的边数int n2array[ESIZE];};int n=0; //边Edge edge[SIZE];int result = LARGENUMBER;int isuse[SIZE] = {0};ifstream fin("fence6.in");ofstream fout("fence6.out");//是否是bool ispoint1(int now, int last){for (int i=0; i < edge[now].n1s; i ++){if (edge[now].n1array[i] == last){return true;}//end if}//end forreturn false;}//深度遍历搜索解void fence(int start, int last, int now, int load){//剪枝if (load >= result){return;}else{int * p;int length;if (ispoint1(now, last)){p = edge[now].n2array;length = edge[now].n2s;}//end if ispoint1else{p = edge[now].n1array;length = edge[now].n1s;}//end if...else..load += edge[now].ls;isuse[now] = 1;for (int i=0; i < length; i ++ ){int index = edge[p[i]].s;if (index == start ){if (ispoint1(start, now)){result = result < load ? result : load;}//end if}//end 形成闭合的路径else{if (isuse[index] == 0){fence(start, now, index, load);}}//递归}//end forisuse[now] = 0;}//end else}int main(){//输入数据fin >> n;for (int i=0; i < n; i ++){int index ;fin >> index;edge[index].s = index;fin>>edge[index].ls >> edge[index].n1s >> edge[index].n2s;//输入端点1的边数for (int j=0; j < edge[index].n1s; j ++){fin >> edge[index].n1array[j];}//输入端点2的边数for (int j=0; j< edge[index].n2s; j ++){fin >> edge[index].n2array[j];}//end for 2}//end for ifor(int i=1; i < SIZE; i ++){if (edge[i].s == i){for (int j =0; j < edge[i].n2s; j ++){isuse[i] = 1;fence(i, i, edge[i].n2array[j], edge[i].ls);}//end for j}//end if}//end for ifout<< result <<endl;return 0;}

    发现自己的回溯法，使用的有点心得了，哈哈……再接再厉，一遍就AC了。

    Executing... Test 1: TEST OK [0.000 secs, 3024 KB] Test 2: TEST OK [0.000 secs, 3024 KB] Test 3: TEST OK [0.000 secs, 3024 KB] Test 4: TEST OK [0.011 secs, 3024 KB] Test 5: TEST OK [0.000 secs, 3024 KB] Test 6: TEST OK [0.011 secs, 3024 KB] Test 7: TEST OK [0.011 secs, 3024 KB] Test 8: TEST OK [0.000 secs, 3024 KB] Test 9: TEST OK [0.000 secs, 3024 KB]All tests OK.YOUR PROGRAM ('fence6') WORKED FIRST TIME! That's fantastic-- and a rare thing. Please accept these special automatedcongratulations.

    太感动了。^_^