android-unlock-patterns.py

# Given an Android 3x3 key lock screen and two integers m and n, where 1 ≤ m ≤ n ≤ 9, count the total number of unlock patterns of the Android lock screen, which consist of minimum of m keys and maximum n keys.
#
# Rules for a valid pattern:
#
# Each pattern must connect at least m keys and at most n keys.
# All the keys must be distinct.
# If the line connecting two consecutive keys in the pattern passes through any other keys, the other keys must have previously selected in the pattern. No jumps through non selected key is allowed.
# The order of keys used matters.
#
#
# \
#
# Explanation:
#
# | 1 | 2 | 3 |
# | 4 | 5 | 6 |
# | 7 | 8 | 9 |
#
# Invalid move: 4 - 1 - 3 - 6 
# Line 1 - 3 passes through key 2 which had not been selected in the pattern.
#
# Invalid move: 4 - 1 - 9 - 2
# Line 1 - 9 passes through key 5 which had not been selected in the pattern.
#
# Valid move: 2 - 4 - 1 - 3 - 6
# Line 1 - 3 is valid because it passes through key 2, which had been selected in the pattern
#
# Valid move: 6 - 5 - 4 - 1 - 9 - 2
# Line 1 - 9 is valid because it passes through key 5, which had been selected in the pattern.
#
# Example:
# Given m = 1, n = 1, return 9.


# V0 

# V1 
# https://blog.csdn.net/qq508618087/article/details/51758481
# IDEA : DP
# C++
# class Solution {
# public:
#     int DFS(int m, int n, int len, int num)
#     {
#         int cnt = 0;
#         if(len >= m) cnt++;
#         if(++len > n) return cnt;
#         visited[num] = true;
#         for(int i = 1; i<= 9; i++)
#             if(!visited[i] && visited[hash[num][i]])
#                 cnt += DFS(m, n, len, i);
#         visited[num] = false;
#         return cnt;
#     }
#   
#     int numberOfPatterns(int m, int n) {
#         if(m < 1 || n < 1) return 0;
#         visited.resize(10, false);
#         visited[0] = true;
#         hash.resize(10, vector<int>(10, 0));
#         hash[1][3] = hash[3][1] = 2;
#         hash[1][7] = hash[7][1] = 4;
#         hash[3][9] = hash[9][3] = 6;
#         hash[7][9] = hash[9][7] = 8;
#         hash[2][8] = hash[8][2] = hash[4][6] = hash[6][4] = 5;
#         hash[1][9] = hash[9][1] = hash[3][7] = hash[7][3] = 5;
#         return DFS(m, n, 1, 1)*4 + DFS(m, n, 1, 2)*4 + DFS(m, n, 1, 5);
#     }
# private:
#     vector<bool> visited;
#     vector<vector<int>> hash;
# };

# V2 
# Time:  O(9^2 * 2^9)
# Space: O(9 * 2^9)
# DP solution.
class Solution(object):
    def numberOfPatterns(self, m, n):
        """
        :type m: int
        :type n: int
        :rtype: int
        """
        def merge(used, i):
            return used | (1 << i)

        def number_of_keys(i):
            number = 0
            while i > 0:
                i &= i - 1
                number += 1
            return number

        def contain(used, i):
            return bool(used & (1 << i))

        def convert(i, j):
            return 3 * i + j

        # dp[i][j]: i is the set of the numbers in binary representation,
        #           dp[i][j] is the number of ways ending with the number j.
        dp = [[0] * 9 for _ in range(1 << 9)]
        for i in range(9):
            dp[merge(0, i)][i] = 1

        res = 0
        for used in range(len(dp)):
            number = number_of_keys(used)
            if number > n:
                continue

            for i in range(9):
                if not contain(used, i):
                    continue

                if m <= number <= n:
                    res += dp[used][i]

                x1, y1 = divmod(i, 3)
                for j in range(9):
                    if contain(used, j):
                        continue

                    x2, y2 = divmod(j, 3)
                    if ((x1 == x2 and abs(y1 - y2) == 2) or
                        (y1 == y2 and abs(x1 - x2) == 2) or
                        (abs(x1 - x2) == 2 and abs(y1 - y2) == 2)) and \
                       not contain(used,
                                   convert((x1 + x2) // 2, (y1 + y2) // 2)):
                            continue

                    dp[merge(used, j)][j] += dp[used][i]

        return res


# Time:  O(9^2 * 2^9)
# Space: O(9 * 2^9)
# DP solution.
class Solution2(object):
    def numberOfPatterns(self, m, n):
        """
        :type m: int
        :type n: int
        :rtype: int
        """
        def merge(used, i):
            return used | (1 << i)

        def number_of_keys(i):
            number = 0
            while i > 0:
                i &= i - 1
                number += 1
            return number

        def exclude(used, i):
            return used & ~(1 << i)

        def contain(used, i):
            return bool(used & (1 << i))

        def convert(i, j):
            return 3 * i + j

        # dp[i][j]: i is the set of the numbers in binary representation,
        #            d[i][j] is the number of ways ending with the number j.
        dp = [[0] * 9 for _ in range(1 << 9)]
        for i in range(9):
            dp[merge(0, i)][i] = 1

        res = 0
        for used in range(len(dp)):
            number = number_of_keys(used)
            if number > n:
                continue

            for i in range(9):
                if not contain(used, i):
                    continue

                x1, y1 = divmod(i, 3)
                for j in range(9):
                    if i == j or not contain(used, j):
                        continue

                    x2, y2 = divmod(j, 3)
                    if ((x1 == x2 and abs(y1 - y2) == 2) or
                        (y1 == y2 and abs(x1 - x2) == 2) or
                        (abs(x1 - x2) == 2 and abs(y1 - y2) == 2)) and \
                       not contain(used,
                                   convert((x1 + x2) // 2, (y1 + y2) // 2)):
                            continue

                    dp[used][i] += dp[exclude(used, i)][j]

                if m <= number <= n:
                    res += dp[used][i]

        return res


# Time:  O(9!)
# Space: O(9)
# Backtracking solution. (TLE)
class Solution_TLE(object):
    def numberOfPatterns(self, m, n):
        """
        :type m: int
        :type n: int
        :rtype: int
        """
        def merge(used, i):
            return used | (1 << i)

        def contain(used, i):
            return bool(used & (1 << i))

        def convert(i, j):
            return 3 * i + j

        def numberOfPatternsHelper(m, n, level, used, i):
            number = 0
            if level > n:
                return number

            if m <= level <= n:
                number += 1

            x1, y1 = divmod(i, 3)
            for j in range(9):
                if contain(used, j):
                    continue

                x2, y2 = divmod(j, 3)
                if ((x1 == x2 and abs(y1 - y2) == 2) or
                    (y1 == y2 and abs(x1 - x2) == 2) or
                    (abs(x1 - x2) == 2 and abs(y1 - y2) == 2)) and \
                   not contain(used,
                               convert((x1 + x2) // 2, (y1 + y2) // 2)):
                        continue

                number += numberOfPatternsHelper(m, n, level + 1, merge(used, j), j)

            return number

        number = 0
        # 1, 3, 7, 9
        number += 4 * numberOfPatternsHelper(m, n, 1, merge(0, 0), 0)
        # 2, 4, 6, 8
        number += 4 * numberOfPatternsHelper(m, n, 1, merge(0, 1), 1)
        # 5
        number += numberOfPatternsHelper(m, n, 1, merge(0, 4), 4)
        return number