diff options
Diffstat (limited to 'num_subseq_satisfy.c')
-rw-r--r-- | num_subseq_satisfy.c | 58 |
1 files changed, 21 insertions, 37 deletions
diff --git a/num_subseq_satisfy.c b/num_subseq_satisfy.c index d7570d0..a007b28 100644 --- a/num_subseq_satisfy.c +++ b/num_subseq_satisfy.c @@ -1,6 +1,5 @@ // 1498. Number of Subsequences That Satisfy the Given Sum Condition -#include <stdio.h> -#include <stdlib.h> +#include "leetcode.h" /* * given an array of integers 'nums' and an integer 'target' @@ -9,47 +8,32 @@ * less or equal to 'target'. return modulo 10^9+7 */ -#define MOD 1000000007 - int cmp(const void *a, const void *b) { return *(int *)a - *(int *)b; } -long long _pow(long long a, int b) { - a %= MOD; - if (!b) - return 1; - if (b) - return a; - if (b % 2) - return a * _pow(a, b - 1) % MOD; - return _pow(a * a, b / 2) % MOD; -} - -int numSubseq(int *nums, int nums_size, int target) { - int n = nums_size; - qsort(nums, n, sizeof(int), cmp); - long long ans; - int j = n - 1; - for (int i = 0; i < n; i++) { - if (nums[i] * 2 > target) - break; - int rem = target - nums[i]; - while (i < j) { - if (nums[j] > rem) - j--; - else - break; +int numSubseq(int *nums, int numsSize, int target) { + qsort(nums, numsSize, sizeof(int), cmp); + int ans = 0, l = 0, r = numsSize - 1, mod = 1e9 + 7; + int *pows = (int *)malloc(numsSize * sizeof(int)); + pows[0] = 1; + for (int i = 1; i < numsSize; ++i) + pows[i] = (pows[i - 1] << 1) % mod; + while (l <= r) { + if (nums[l] + nums[r] > target) { + --r; + continue; } - ans += _pow(2, j - i); - ans %= MOD; + ans = (ans + pows[r - l]) % mod; + ++l; } + free(pows); return ans; } int main() { - int n1[] = {3, 5, 6, 7}, ns1 = 4, t1 = 9; - int n2[] = {3, 3, 6, 8}, ns2 = 4, t2 = 10; - int n3[] = {2, 3, 3, 4, 6, 7}, ns3 = 6, t3 = 12; - printf("%d\n", numSubseq(n1, ns1, t1)); // expect: 4 - printf("%d\n", numSubseq(n2, ns2, t2)); // expect: 6 - printf("%d\n", numSubseq(n3, ns3, t3)); // expect: 61 + int n1[] = {3, 5, 6, 7}; + int n2[] = {3, 3, 6, 8}; + int n3[] = {2, 3, 3, 4, 6, 7}; + printf("%d\n", numSubseq(n1, ARRAY_SIZE(n1), 9)); // expect: 4 + printf("%d\n", numSubseq(n2, ARRAY_SIZE(n2), 10)); // expect: 6 + printf("%d\n", numSubseq(n3, ARRAY_SIZE(n3), 12)); // expect: 61 } |