|
| 1 | +""" |
| 2 | +Problem Link: https://practice.geeksforgeeks.org/problems/consecutive-1s-not-allowed1912/1 |
| 3 | + |
| 4 | +Input: |
| 5 | +N = 3 |
| 6 | +Output: 5 |
| 7 | +Explanation: 5 strings are (000, |
| 8 | +001, 010, 100, 101). |
| 9 | + |
| 10 | +Example 2: |
| 11 | +Input: |
| 12 | +N = 2 |
| 13 | +Output: 3 |
| 14 | +Explanation: 3 strings are |
| 15 | +(00,01,10). |
| 16 | + |
| 17 | +Your Task: |
| 18 | +Complete the function countStrings() which takes single integer n, as input parameters and returns an integer denoting the answer. |
| 19 | +You don't to print answer or take inputs. |
| 20 | + |
| 21 | +Expected Time Complexity: O(N) |
| 22 | +Expected Auxiliary Space: O(N) |
| 23 | + |
| 24 | +Constraints: |
| 25 | +1 ≤ N ≤ 105 |
| 26 | +""" |
| 27 | +class Solution: |
| 28 | + |
| 29 | + def countStrings(self,n): |
| 30 | + zero_count = 1 |
| 31 | + one_count = 1 |
| 32 | + |
| 33 | + for i in range(1, n): |
| 34 | + zero_count, one_count = (zero_count + one_count) % 1000000007, zero_count |
| 35 | + |
| 36 | + return (zero_count + one_count) % 1000000007 |
| 37 | + |
| 38 | + |
| 39 | +# TLE |
| 40 | +class Solution1: |
| 41 | + |
| 42 | + def countStrings(self,n): |
| 43 | + return len(self.helper(n)) |
| 44 | + |
| 45 | + def helper(self, n): |
| 46 | + if n == 1: |
| 47 | + return ["0", "1"] |
| 48 | + numbers = self.helper(n-1) |
| 49 | + res = [] |
| 50 | + for num in numbers: |
| 51 | + res.append(num + "0") |
| 52 | + if num[-1] != "1": |
| 53 | + res.append(num + "1") |
| 54 | + return res |
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