1. 程式人生 > >【Uva816】[BFS]進階題目的深度思考與解析

【Uva816】[BFS]進階題目的深度思考與解析

char* str="ABCD"

利用 return strchr(str,char)-

#include<cstdio>
#include<cstring>
#include<vector>
#include<queue>
using namespace std;

struct Node {
  int r, c, dir; // 站在(r,c),面朝方向dir(0~3分別表示N, E, S, W)
  Node(int r=0, int c=0, int dir=0):r(r),c(c),dir(dir) {}
};

const int maxn = 10
; const char* dirs = "NESW"; // 順時針旋轉 const char* turns = "FLR"; int has_edge[maxn][maxn][4][3]; int d[maxn][maxn][4]; Node p[maxn][maxn][4]; int r0, c0, dir, r1, c1, r2, c2; int dir_id(char c) { return strchr(dirs, c) - dirs; } int turn_id(char c) { return strchr(turns, c) - turns; } const int dr[] = {-1
, 0, 1, 0}; const int dc[] = {0, 1, 0, -1}; Node walk(const Node& u, int turn) { int dir = u.dir; if(turn == 1) dir = (dir + 3) % 4; // 逆時針 if(turn == 2) dir = (dir + 1) % 4; // 順時針 return Node(u.r + dr[dir], u.c + dc[dir], dir); } bool inside(int r, int c) { return r >= 1 && r <= 9
&& c >= 1 && c <= 9; } bool read_case() { char s[99], s2[99]; if(scanf("%s%d%d%s%d%d", s, &r0, &c0, s2, &r2, &c2) != 6) return false; printf("%s\n", s); dir = dir_id(s2[0]); r1 = r0 + dr[dir]; c1 = c0 + dc[dir]; memset(has_edge, 0, sizeof(has_edge)); for(;;) { int r, c; scanf("%d", &r); if(r == 0) break; scanf("%d", &c); while(scanf("%s", s) == 1 && s[0] != '*') { for(int i = 1; i < strlen(s); i++) has_edge[r][c][dir_id(s[0])][turn_id(s[i])] = 1; } } return true; } void print_ans(Node u) { // 從目標結點逆序追溯到初始結點 vector<Node> nodes; for(;;) { nodes.push_back(u); if(d[u.r][u.c][u.dir] == 0) break; u = p[u.r][u.c][u.dir]; } nodes.push_back(Node(r0, c0, dir)); // 列印解,每行10個 int cnt = 0; for(int i = nodes.size()-1; i >= 0; i--) { if(cnt % 10 == 0) printf(" "); printf(" (%d,%d)", nodes[i].r, nodes[i].c); if(++cnt % 10 == 0) printf("\n"); } if(nodes.size() % 10 != 0) printf("\n"); } void solve() { queue<Node> q; memset(d, -1, sizeof(d)); Node u(r1, c1, dir); d[u.r][u.c][u.dir] = 0; q.push(u); while(!q.empty()) { Node u = q.front(); q.pop(); if(u.r == r2 && u.c == c2) { print_ans(u); return; } for(int i = 0; i < 3; i++) { Node v = walk(u, i); if(has_edge[u.r][u.c][u.dir][i] && inside(v.r, v.c) && d[v.r][v.c][v.dir] < 0) { d[v.r][v.c][v.dir] = d[u.r][u.c][u.dir] + 1; p[v.r][v.c][v.dir] = u; q.push(v); } } } printf(" No Solution Possible\n"); } int main() { while(read_case()) { solve(); } return 0; }