uva 216 Getting in Line

递归枚举应用，递归枚举所有可能出现的序列，在递归里面取最优的一组就行了，注意当当前的总长已经超过最小的总长的时候递归就可以回溯了。

#include <stdio.h>#include <math.h>#include <string.h>#include <float.h>struct pos{double x;double y;};struct pos all_pos[10];struct pos serial[10];struct pos min_serial[10];unsigned char visited[10];double min_dis;double get_dis(const struct pos &p1, const struct pos &p2){return sqrt(pow(p1.x-p2.x,2.0)+pow(p1.y-p2.y,2.0));}void dfs(int len, int cur, double cur_dis){int i, j;double dis;if(cur == len+1){if(cur_dis < min_dis){min_dis = cur_dis;for(i=1; i<=len; i++){min_serial[i].x = serial[i].x;min_serial[i].y = serial[i].y;}}}if(cur == 1){for(i=1; i<=len; i++){serial[cur].x = all_pos[i].x;serial[cur].y = all_pos[i].y;visited[i] = 1;dfs(len, cur+1, cur_dis);visited[i] = 0;}}else{for(i=1; i<=len; i++){if(!visited[i]){serial[cur].x = all_pos[i].x;serial[cur].y = all_pos[i].y;visited[i] = 1;dis = get_dis(serial[cur], serial[cur-1]);if(cur_dis+dis<min_dis)dfs(len, cur+1, cur_dis+dis);visited[i] = 0;}}}}void func(int n){int i;memset((void*)visited, 0, sizeof(unsigned char)*10);min_dis = DBL_MAX;dfs(n, 1, 0.0);for(i=2; i<=n; i++){printf("Cable requirement to connect (%.0lf,%.0lf) to (%.0lf,%.0lf) is %.2lf feet.\n", min_serial[i-1].x,min_serial[i-1].y,min_serial[i].x,min_serial[i].y,get_dis(min_serial[i-1], min_serial[i])+16);}printf("Number of feet of cable required is %.2lf.\n", min_dis+16*(n-1));}int main(void){int n;int i;int case_count;//freopen("input.dat", "r", stdin);case_count = 0;while(scanf("%d", &n)){if(!n)break;for(i=1; i<=n; i++)scanf("%lf %lf", &(all_pos[i].x), &(all_pos[i].y));case_count ++;printf("**********************************************************\n");printf("Network #%d\n", case_count);func(n);}return 0;}