bfs分六种情况往下走，模拟倒的过程。
注意退出时必须是两个杯子均为s / 2，而不能是一个杯子，有可能另一半没汇聚到一个杯子里呢。WA了好几次...
#include<cstdio>
#include<iostream>
#include<cstring>
#include<algorithm>
#include<queue>
using namespace std;
const int maxn = 110;
int s, n, m;
struct Node
{int a, b, ss;int step;Node() {}Node(int x, int y, int z, int dep){a = x; b = y; ss = z; step = dep;}
};
bool vis[maxn][maxn][maxn];int bfs()
{queue<Node> q;q.push(Node(0, 0, s, 0));vis[0][0][s] = 1;while(!q.empty()){Node head = q.front();q.pop();int cura = head.a, curb = head.b, curs = head.ss;int step = head.step;//cout << cura << " " << curb << " " << curs << endl;if((cura == s / 2 && curb == s / 2) || (cura == s / 2 && curs == s / 2) || (curb == s / 2 && curs == s / 2)){return step;}int newa, newb, news;if(curs && cura != n){if(curs + cura >= n) //s - > a{newa = n; news = curs + cura - n; newb = curb;}else{newa = curs + cura; news = 0; newb = curb;}if(!vis[newa][newb][news]){q.push(Node(newa, newb, news, step + 1));vis[newa][newb][news] = 1;}}if(curs && curb != m){if(curs + curb >= m) //s - > b{newa = cura; news = curs + curb - m; newb = m;}else{newa = cura; news = 0; newb = curs + curb;}if(!vis[newa][newb][news]){q.push(Node(newa, newb, news, step + 1));vis[newa][newb][news] = 1;}}if(cura && curs != s){if(cura + curs >= s) //a - > s{newa = cura + curs - s; news = s; newb = curb;}else{newa = 0; news = cura + curs; newb = curb;}if(!vis[newa][newb][news]){q.push(Node(newa, newb, news, step + 1));vis[newa][newb][news] = 1;}}if(cura && curb != m){if(cura + curb >= m) //a - > b{newa = cura + curb - m; newb = m; news = curs;}else{newa = 0; newb = cura + curb; news = curs;}if(!vis[newa][newb][news]){q.push(Node(newa, newb, news, step + 1));vis[newa][newb][news] = 1;}}if(curb && curs != s){if(curb + curs >= s) //b - > s{newa = cura; news = s; newb = curb + curs - s;}else{newa = cura; news = curb + curs; newb = 0;}if(!vis[newa][newb][news]){q.push(Node(newa, newb, news, step + 1));vis[newa][newb][news] = 1;}}if(curb && cura != n){if(cura + curb >= n) //b - > a{newa = n; newb = cura + curb - n; news = curs;}else{newa = cura + curb; newb = 0; news = curs;}if(!vis[newa][newb][news]){q.push(Node(newa, newb, news, step + 1));vis[newa][newb][news] = 1;}}}return 0;
}int main()
{while(scanf("%d%d%d", &s, &n, &m) == 3 && (s && n && m)){memset(vis, 0, sizeof(vis));if(s & 1){printf("NO\n"); continue;}int ans = bfs();if(ans) printf("%d\n", ans);else printf("NO\n");}return 0;
}