Breadth-First Search
1. Maze
This is my solution to a problem in SJTU ACM Online Judge:
1 import java.util.*; 2 3 public class Main { 4 public static final int INF = 65535; 5 public static int wid, len; 6 public static char [] map; 7 8 public static int bfs(int x1,int y1,int x2,int y2) { 9 Queue<Integer> q = new LinkedList<Integer>(); 10 boolean [] vis = new boolean[wid*len]; 11 int [] dist = new int[wid*len]; 12 for (int i=0;i<wid;i++) { 13 for (int j=0;j<len;j++) { 14 dist[i*len+j] = INF; 15 } 16 } 17 q.add(new Integer(x1*len+y1)); 18 vis[x1*len+y1] = true; 19 dist[x1*len+y1] = 0; 20 while (dist[x2*len+y2]==INF) { 21 if (q.isEmpty()) { 22 // no such path exists 23 return -1; 24 } 25 int pos = q.poll().intValue(); 26 if (map[pos]=='.') { 27 if (pos%len>0 && !vis[pos-1] && map[pos-1]!='|') { //West 28 q.add(new Integer(pos-1)); 29 vis[pos-1] = true; 30 dist[pos-1] = dist[pos]+1; 31 } 32 if (pos/len>0 && !vis[pos-len] && map[pos-len]!='-') { //North 33 q.add(new Integer(pos-len)); 34 vis[pos-len] = true; 35 dist[pos-len] = dist[pos]+1; 36 } 37 if (pos%len<len-1 && !vis[pos+1] && map[pos+1]!='|') { //East 38 q.add(new Integer(pos+1)); 39 vis[pos+1] = true; 40 dist[pos+1] = dist[pos]+1; 41 } 42 if (pos/len<wid-1 && !vis[pos+len] && map[pos+len]!='-') { //South 43 q.add(new Integer(pos+len)); 44 vis[pos+len] = true; 45 dist[pos+len] = dist[pos]+1; 46 } 47 } else if (map[pos]=='|') { 48 if (pos/len>0 && !vis[pos-len] && map[pos-len]!='-') { //North 49 q.add(new Integer(pos-len)); 50 vis[pos-len] = true; 51 dist[pos-len] = dist[pos]+1; 52 } 53 if (pos/len<wid-1 && !vis[pos+len] && map[pos+len]!='-') { //South 54 q.add(new Integer(pos+len)); 55 vis[pos+len] = true; 56 dist[pos+len] = dist[pos]+1; 57 } 58 } else if (map[pos]=='-') { 59 if (pos%len>0 && !vis[pos-1] && map[pos-1]!='|') { //West 60 q.add(new Integer(pos-1)); 61 vis[pos-1] = true; 62 dist[pos-1] = dist[pos]+1; 63 } 64 if (pos%len<len-1 && !vis[pos+1] && map[pos+1]!='|') { //East 65 q.add(new Integer(pos+1)); 66 vis[pos+1] = true; 67 dist[pos+1] = dist[pos]+1; 68 } 69 } 70 } 71 return dist[x2*len+y2]; 72 } 73 public static void main(String[] args) { 74 Scanner in = new Scanner(System.in); 75 wid = in.nextInt(); 76 len = in.nextInt(); 77 map = new char[wid*len]; 78 int x1=in.nextInt()-1; 79 int y1=in.nextInt()-1; 80 int x2=in.nextInt()-1; 81 int y2=in.nextInt()-1; 82 for (int i=0;i<wid;i++) { 83 String line = in.next(); 84 for (int j=0;j<len;j++) { 85 map[i*len+j]=line.charAt(j); 86 } 87 } 88 in.close(); 89 System.out.println(bfs(x1,y1,x2,y2)); 90 } 91 }
2. The Clocks
This is my solution to the USACO training problem "clocks":
1 import java.io.*; 2 import java.util.*; 3 4 public class clocks { 5 public static BufferedReader input; 6 public static PrintWriter output; 7 8 private static int turn(int state,int pos) { 9 int tmp = state; 10 pos = 8 - pos; 11 tmp &= (3<<pos<<pos); 12 tmp >>= (pos<<1); 13 tmp = ((tmp+1)&3); 14 tmp <<= (pos<<1); 15 state &= (~(3<<pos<<pos)); 16 state |= tmp; 17 return state; 18 } 19 private static int operate(int state,int mode) { 20 switch (mode) { 21 case 1: 22 state = turn(state,0); 23 state = turn(state,1); 24 state = turn(state,3); 25 state = turn(state,4); 26 break; 27 case 2: 28 state = turn(state,0); 29 state = turn(state,1); 30 state = turn(state,2); 31 break; 32 case 3: 33 state = turn(state,1); 34 state = turn(state,2); 35 state = turn(state,4); 36 state = turn(state,5); 37 break; 38 case 4: 39 state = turn(state,0); 40 state = turn(state,3); 41 state = turn(state,6); 42 break; 43 case 5: 44 state = turn(state,1); 45 state = turn(state,3); 46 state = turn(state,4); 47 state = turn(state,5); 48 state = turn(state,7); 49 break; 50 case 6: 51 state = turn(state,2); 52 state = turn(state,5); 53 state = turn(state,8); 54 break; 55 case 7: 56 state = turn(state,3); 57 state = turn(state,4); 58 state = turn(state,6); 59 state = turn(state,7);; 60 break; 61 case 8: 62 state = turn(state,6); 63 state = turn(state,7); 64 state = turn(state,8); 65 break; 66 case 9: 67 state = turn(state,4); 68 state = turn(state,5); 69 state = turn(state,7); 70 state = turn(state,8); 71 } 72 return state; 73 } 74 private static boolean threeTimes(int path,int mode) { 75 path &= (3<<mode<<mode); 76 path >>= (mode<<1); 77 return (path==3); 78 } 79 private static void printPath(int path) { 80 // Print the move sequence except the last one 81 for (int i=1;i<=9;i++) { 82 int cnt = (3<<i<<i); 83 cnt &= path; 84 cnt >>= (i<<1); 85 for (int j=0;j<cnt;j++) { 86 output.print(i+" "); 87 } 88 } 89 } 90 private static void bfs(int clk) { 91 // Breadth-First Search in a State Space: 92 // state and path are both coded into integers 93 Queue<Integer> pathQ = new LinkedList<Integer>(); 94 Queue<Integer> stateQ = new LinkedList<Integer>(); 95 boolean [] vis = new boolean[1<<18]; 96 pathQ.add(new Integer(0)); 97 stateQ.add(new Integer(clk)); 98 vis[clk] = true; 99 while (!pathQ.isEmpty()) { 100 int path = pathQ.poll().intValue(); 101 int state = stateQ.poll().intValue(); 102 for (int i=1;i<=9;i++) { 103 if (threeTimes(path,i)) { 104 // each move can be operated no more than 3 times 105 continue; 106 } 107 int newState = operate(state,i); 108 if (newState==0) { 109 // print the path when reaching the destination 110 printPath(path); 111 output.println(i); 112 return; 113 } else if (!vis[newState]) { 114 vis[newState] = true; 115 stateQ.add(new Integer(newState)); 116 pathQ.add(new Integer(path+(1<<i<<i))); 117 } 118 } 119 } 120 } 121 public static void main(String [] args) throws IOException { 122 input = new BufferedReader(new FileReader("clocks.in")); 123 int clk = 0; 124 for (int i=0;i<3;i++) { 125 StringTokenizer str = new StringTokenizer(input.readLine()); 126 for (int j=0;j<3;j++) { 127 clk = (clk<<2)+((12-Integer.parseInt(str.nextToken()))&3); 128 } 129 } 130 input.close(); 131 output = new PrintWriter(new FileWriter("clocks.out")); 132 if (clk==0) { 133 output.println(); 134 } else { 135 bfs(clk); 136 } 137 output.close(); 138 } 139 }
