Light 1039 - A Toy Company (bfs)
2015-08-11 22:27
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题意
给一个初始串和目标串,一次只能变换相邻的字母,问最少变换几次,有一些禁止变换的排列。思路
因为总共才3个字母,所以可以直接用数字表示一个单词。然后处理一下禁止的单词,丢set里。
然后就开始bfs。
这题的思路很简单,不过写得很蛋疼。。不知道为什么。把状态push到队列的时候的写法换了很多种才写出来。。
这题也可以建图跑最短路。不过感觉跑不跑都差不多,因为边权都是1.
代码
#include <stack> #include <cstdio> #include <list> #include <cassert> #include <set> #include <fstream> #include <iostream> #include <string> #include <sstream> #include <vector> #include <queue> #include <functional> #include <cstring> #include <algorithm> #include <cctype> #pragma comment(linker, "/STACK:102400000,102400000") #include <string> #include <map> #include <cmath> //#include <ext/pb_ds/assoc_container.hpp> //#include <ext/pb_ds/hash_policy.hpp> using namespace std; //using namespace __gnu_pbds; #define LL long long #define ULL unsigned long long #define SZ(x) (int)x.size() #define Lowbit(x) ((x) & (-x)) #define MP(a, b) make_pair(a, b) #define MS(p, num) memset(p, num, sizeof(p)) #define PB push_back #define X first #define Y second #define ROP freopen("input.txt", "r", stdin); #define MID(a, b) (a + ((b - a) >> 1)) #define LC rt << 1, l, mid #define RC rt << 1|1, mid + 1, r #define LRT rt << 1 #define RRT rt << 1|1 #define FOR(i, a, b) for (int i=(a); (i) < (b); (i)++) #define FOOR(i, a, b) for (int i = (a); (i)<=(b); (i)++) #define TRAVERSAL(u, i) for (int i = head[u]; i != -1; i = edge[i].nxt) const double PI = acos(-1.0); const int INF = 0x3f3f3f3f; const double eps = 1e-8; const int MAXN = 1e7+10; const int MOD = 1e9+7; const int dir[][2] = { {-1, 0}, {1, 0}, {0, -1}, {0, 1} }; const int seed = 131; int cases = 0; typedef pair<int, int> pii; int arr[3], vis[26*26*26]; queue<int> Q; string start, target; set<int> mp; void dfs(int u, int tar, int sum, int cnt) { if (sum > 26*26*26) return; if (u == 3) { if (!vis[sum] && !mp.count(sum)) { vis[sum] = cnt+1; Q.push(sum); } return; } if (u == tar) { dfs(u+1, tar, sum*26 + (arr[u]+1)%26, cnt); dfs(u+1, tar, sum*26 + (arr[u]-1+26)%26, cnt); } else dfs(u+1, tar, sum*26 + arr[u], cnt); } void Push(int u, int cnt) { arr[2] = u % 26; u /= 26; arr[1] = u % 26; u /= 26; arr[0] = u; for (int i = 0; i <= 2; i++) //变换第i个字母 dfs(0, i, 0, cnt); } int Hash(char a, char b, char c) { int ret = 0; ret = a-'a'; ret *= 26; ret += b-'a'; ret *= 26; ret += c-'a'; return ret; } void bfs() { int ed = Hash(target[0], target[1], target[2]); Q.push(Hash(start[0], start[1], start[2])); while (!Q.empty()) { int u = Q.front(); Q.pop(); if (mp.count(u)) continue; if (u == ed) { printf("%d\n", vis[u]); return; } Push(u, vis[u]); } printf("-1\n"); } int main() { //ROP; int T; scanf("%d", &T); while (T--) { printf("Case %d: ", ++cases); mp.clear(); while (!Q.empty()) Q.pop(); MS(vis, 0); cin >> start >> target; int n; scanf("%d", &n); while (n--) { string a, b, c; cin >> a >> b >> c; FOR(i, 0, SZ(a)) FOR(j, 0, SZ(b)) FOR(k, 0, SZ(c)) mp.insert(Hash(a[i], b[j], c[k])); } bfs(); } return 0; }
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