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Diffstat (limited to 'num_ways_reorder_array.cpp')
-rw-r--r-- | num_ways_reorder_array.cpp | 57 |
1 files changed, 0 insertions, 57 deletions
diff --git a/num_ways_reorder_array.cpp b/num_ways_reorder_array.cpp deleted file mode 100644 index 9adcb55..0000000 --- a/num_ways_reorder_array.cpp +++ /dev/null @@ -1,57 +0,0 @@ -// 1569. Number of Ways to Reorder Array to Get Same BST -#include "leetcode.h" - -/* - * given an array 'nums' that represents a permutation of integers from '1 to - * n'. we are going to construct a binary search tree (BST) by inserting the - * elements of 'nums' in order into an initially empty BST. find the number of - * different ways to reorder 'nums' so that the constructed BST is identical to - * that formed from the original array 'nums'. for example given 'nums = - * [2,1,3]', we will have 2 as the root, 1 as a left child, and three as a right - * child. the array [2,3,1] also yields the same BST, but '[3,2,1]' yields a - * different BST. return the number of ways to reorder 'nums' such that the BST - * formed is identical to the original BST formed from 'nums'. since the answer - * may be large, return it modulo 10^9+7 - */ - -class Solution { - int mod = 1e+9 + 7; - long l[10001][10001] = {0}; - bool init = false; - long combination(int n, int r) { - if (init) - return l[n][r]; - l[0][0] = 1; - for (int i = 1; i < 1001; i++) { - l[i][0] = 1; - for (int j = 1; j < i + 1; j++) - l[i][j] = (l[i - 1][j - 1] + l[i - 1][j]) % mod; - } - init = true; - return l[n][r]; - } - long dfs(vector<int> &nums) { - if (nums.size() < 3) - return 1; - vector<int> l, r; - for (auto n : nums) { - if (n > nums[0]) - l.push_back(n); - if (n < nums[0]) - r.push_back(n); - } - long c = combination(l.size() + r.size(), l.size()); - return c * dfs(l) % mod * dfs(r) % mod; - } - -public: - int numOfWays(vector<int> &nums) { return dfs(nums) - 1; } -}; - -int main() { - Solution obj; - vector<int> n1 = {2, 1, 3}, n2 = {3, 4, 5, 1, 2}, n3 = {1, 2, 3}; - printf("%d\n", obj.numOfWays(n1)); // expect: 1 - printf("%d\n", obj.numOfWays(n2)); // expect: 5 - printf("%d\n", obj.numOfWays(n3)); // expect: 0 -} |