G面经prepare: Android Phone Unlock Pattern
1 2 3 4 5 6 7 8 9 只有中间没有其他键的两个键才能相连，比如1可以连 2 4 5 6 8 但不能连 3 7 9 但是如果中间键被使用了，那就可以连，比如5已经被使用了，那1就可以连9 每个键只能用一次，给定一个长度L，求问有多少unique path with length L
Backtracking: 我的code不光可以知道数目，还可以打印所有Pattern
1 package AndroidUnlockPattern; 2 import java.util.*; 3 4 public class Solution { 5 int res = 0; 6 HashSet<Integer> set = new HashSet<Integer>(); 7 static ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>(); 8 ArrayList<Integer> path = new ArrayList<Integer>(); 9 10 public int calculate(int L) { 11 for (int i=1; i<=9; i++) { 12 set.add(i); 13 } 14 HashSet<Integer> visited = new HashSet<Integer>(); 15 helper(0, 0, L, visited); 16 return res; 17 } 18 19 public void helper(int cur, int pos, int L, HashSet<Integer> visited) { 20 if (pos == L) { 21 res++; 22 result.add(new ArrayList<Integer>(path)); 23 return; 24 } 25 for (int elem : set) { 26 if (visited.contains(elem)) continue; 27 if (cur == 1) { 28 if (elem==3 && !visited.contains(2)) continue; 29 if (elem==7 && !visited.contains(4)) continue; 30 if (elem==9 && !visited.contains(5)) continue; 31 } 32 else if (cur == 2) { 33 if (elem==8 && !visited.contains(5)) continue; 34 } 35 else if (cur == 3) { 36 if (elem==1 && !visited.contains(2)) continue; 37 if (elem==7 && !visited.contains(5)) continue; 38 if (elem==9 && !visited.contains(6)) continue; 39 } 40 else if (cur == 4) { 41 if (elem == 6 && !visited.contains(5)) continue; 42 } 43 else if (cur == 6) { 44 if (elem == 4 && !visited.contains(5)) continue; 45 } 46 else if (cur == 7) { 47 if (elem==1 && !visited.contains(4)) continue; 48 if (elem==3 && !visited.contains(5)) continue; 49 if (elem==9 && !visited.contains(8)) continue; 50 } 51 else if (cur == 8) { 52 if (elem==2 && !visited.contains(5)) continue; 53 } 54 else if (cur == 9) { 55 if (elem==1 && !visited.contains(5)) continue; 56 if (elem==3 && !visited.contains(6)) continue; 57 if (elem==7 && !visited.contains(8)) continue; 58 } 59 visited.add(elem); 60 path.add(elem); 61 helper(elem, pos+1, L, visited); 62 visited.remove(elem); 63 path.remove(path.size()-1); 64 } 65 } 66 67 68 /** 69 * @param args 70 */ 71 public static void main(String[] args) { 72 // TODO Auto-generated method stub 73 Solution sol = new Solution(); 74 int res = sol.calculate(3); 75 System.out.println(res); 76 for (ArrayList<Integer> each : result) { 77 System.out.println(each); 78 } 79 } 80 81 }
