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-rw-r--r-- | reverse_pairs.c | 52 | ||||
-rw-r--r-- | reverse_pairs.py | 49 |
2 files changed, 101 insertions, 0 deletions
diff --git a/reverse_pairs.c b/reverse_pairs.c new file mode 100644 index 0000000..261a9cf --- /dev/null +++ b/reverse_pairs.c @@ -0,0 +1,52 @@ +// 493. Reverse Pairs +#include "leetcode.h" + +/* + * given an integer array 'nums', return the number of reverse pairs in the + * array. a reverse pair is a pair '(i, j)' where '0 <= i < j < nums.len' and + * 'nums[i] > 2 * nums[j]' + */ + +int merge_cnt(int *arr, int *tmp, int left, int mid, int right) { + int i = left, j = mid + 1, k = left, cnt = 0; + while (i <= mid && j <= right) { + if ((long long)arr[i] > 2 * (long long)arr[j]) { + cnt += (mid - i + 1); + j++; + } else + i++; + } + i = left; + j = mid + 1; + while (i <= mid && j <= right) + tmp[k++] = arr[i] <= arr[j] ? arr[i++] : arr[j++]; + while (i <= mid) + tmp[k++] = arr[i++]; + while (j <= right) + tmp[k++] = arr[j++]; + for (int l = left; l <= right; l++) + arr[l] = tmp[l]; + return cnt; +} + +int sort_merge_cnt(int *arr, int *tmp, int left, int right) { + int cnt = 0; + if (left < right) { + int mid = left + (right - left) / 2; + cnt += sort_merge_cnt(arr, tmp, left, mid); + cnt += sort_merge_cnt(arr, tmp, mid + 1, right); + cnt += merge_cnt(arr, tmp, left, mid, right); + } + return cnt; +} + +int reversePairs(int *nums, int numsSize) { + int *tmp = (int *)malloc(numsSize * sizeof(int)); + return sort_merge_cnt(nums, tmp, 0, numsSize - 1); +} + +int main() { + int n1[] = {1, 3, 2, 3, 1}, n2[] = {2, 4, 3, 5, 1}; + printf("%d\n", reversePairs(n1, ARRAY_SIZE(n1))); // expect: 2 + printf("%d\n", reversePairs(n2, ARRAY_SIZE(n2))); // expect: 3 +} diff --git a/reverse_pairs.py b/reverse_pairs.py new file mode 100644 index 0000000..3ee2dfe --- /dev/null +++ b/reverse_pairs.py @@ -0,0 +1,49 @@ +# 493. Reverse Pairs + +""" +given an integer array 'nums', return the number of reverse pairs in the +array. a reverse pair is a pair '(i, j)' where '0 <= i < j < nums.len' and +'nums[i] > 2 nums[j]' +""" + + +class Bits: + def __init__(self, n): + self.n = n + 1 + self.sums = [0] * self.n + + def update(self, i, delta): + while i < self.n: + self.sums[i] += delta + i += i & (-i) + + def query(self, i): + res = 0 + while i > 0: + res += self.sums[i] + i -= i & (-i) + return res + + +class Solution(object): + def reversePairs(self, nums): + """ + :type nums: List[int] + :rtype: int + """ + new_nums = nums + [x * 2 for x in nums] + sorted_set = sorted(list(set(new_nums))) + tree = Bits(len(sorted_set)) + ans, ranks = 0, {} + for i, n in enumerate(sorted_set): + ranks[n] = i + 1 + for n in nums[::-1]: + ans += tree.query(ranks[n] - 1) + tree.update(ranks[n * 2], 1) + return ans + + +if __name__ == "__main__": + obj = Solution() + print(obj.reversePairs(nums=[1, 3, 2, 3, 1])) + print(obj.reversePairs(nums=[2, 4, 3, 5, 1])) |