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author | jack <[email protected]> | 2024-06-14 13:13:15 -0600 |
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committer | jack <[email protected]> | 2024-06-14 13:13:15 -0600 |
commit | d343a3b18dbaca9297d4f7b2280c4a16f0a5c8aa (patch) | |
tree | 96df922dae2a5073d9a50ea70c7aae6aa37e3ebe /count_num_fair_pairs.c | |
download | leetcode-d343a3b18dbaca9297d4f7b2280c4a16f0a5c8aa.tar.gz leetcode-d343a3b18dbaca9297d4f7b2280c4a16f0a5c8aa.zip |
initial
Diffstat (limited to 'count_num_fair_pairs.c')
-rw-r--r-- | count_num_fair_pairs.c | 57 |
1 files changed, 57 insertions, 0 deletions
diff --git a/count_num_fair_pairs.c b/count_num_fair_pairs.c new file mode 100644 index 0000000..80d26f1 --- /dev/null +++ b/count_num_fair_pairs.c @@ -0,0 +1,57 @@ +// 2563. Count the Number of Fair Pairs +#include "leetcode.h" + +/* + * given a 0 indexed integer array 'nums' of size 'n', and two integers 'lower' + * and 'upper', return the number of fair pairs. pair '(i, j)' is fair is '0 <= + * i < j < n' and 'lower <= nums[i] + nums[j] <= upper' + */ + +int cmp(const void *a, const void *b) { return *(int *)a - *(int *)b; } + +int bs_lower(int *nums, int n, int left, int right, int lower) { + int l = left, r = right; + if (nums[r] < lower) + return -1; + while (l < r) { + int m = l + (r - l) / 2; + if (nums[m] < lower) + l = m + 1; + else + r = m; + } + return l; +} + +int bs_upper(int *nums, int n, int left, int right, int upper) { + int l = left, r = right; + if (nums[l] > upper) + return -1; + while (l < r) { + int m = r - (r - l) / 2; + if (nums[m] > upper) + r = m - 1; + else + l = m; + } + return l; +} + +long long countFairPairs(int *nums, int numsSize, int lower, int upper) { + int n = numsSize; + long long ans = 0; + qsort(nums, n, sizeof(int), cmp); + for (int i = 0; i < n - 1; i++) { + int left = bs_lower(nums, n, i + 1, n - 1, lower - nums[i]); + int right = bs_upper(nums, n, i + 1, n - 1, upper - nums[i]); + if (left != -1 && right != -1) + ans += right - left + 1; + } + return ans; +} + +int main() { + int n1[] = {0, 1, 7, 4, 4, 5}, n2[] = {1, 7, 9, 2, 5}; + printf("%lld\n", countFairPairs(n1, ARRAY_SIZE(n1), 3, 6)); // expect: 6 + printf("%lld\n", countFairPairs(n2, ARRAY_SIZE(n2), 11, 11)); // expect: 1 +} |