LeetCode 247: Strobogrammatic Number II
LeetCode 247 Solution Explanation
Explanation:
To solve this problem, we can use a recursive approach to generate all strobogrammatic numbers of length n. We can start with the base cases for n = 0 and n = 1, and then recursively build strobogrammatic numbers of length n based on the numbers of length n-2.
Algorithm:
- Initialize a list to store the strobogrammatic numbers of length
n. - Handle the base cases for
n = 0andn = 1. - Recursively generate strobogrammatic numbers of length
n-2. - For each pair of strobogrammatic numbers of length
n-2, add the valid strobogrammatic numbers of lengthnby adding0and1to both ends of the pair. - If
nis not equal to the desired length, add8at the center if it is not the last digit. - Return the list of strobogrammatic numbers of length
n.
Time Complexity: O(5^(n/2)) where n is the length of the strobogrammatic numbers. Space Complexity: O(5^(n/2)) for storing the result.
:
LeetCode 247 Solutions in Java, C++, Python
class Solution {
public List<String> findStrobogrammatic(int n) {
return helper(n, n);
}
private List<String> helper(int n, int m) {
if (n == 0) return new ArrayList<>(Arrays.asList(""));
if (n == 1) return new ArrayList<>(Arrays.asList("0", "1", "8"));
List<String> list = helper(n - 2, m);
List<String> res = new ArrayList<>();
for (String s : list) {
if (n != m) res.add("0" + s + "0");
res.add("1" + s + "1");
res.add("6" + s + "9");
res.add("8" + s + "8");
res.add("9" + s + "6");
}
return res;
}
}Interactive Code Editor for LeetCode 247
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