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authorjack <[email protected]>2024-06-14 13:13:15 -0600
committerjack <[email protected]>2024-06-14 13:13:15 -0600
commitd343a3b18dbaca9297d4f7b2280c4a16f0a5c8aa (patch)
tree96df922dae2a5073d9a50ea70c7aae6aa37e3ebe /num_subseq_satisfy.c
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+// 1498. Number of Subsequences That Satisfy the Given Sum Condition
+#include <stdio.h>
+#include <stdlib.h>
+
+/*
+ * given an array of integers 'nums' and an integer 'target'
+ * return the numbe of non-empty subsequences of 'nums' such
+ * that the sum of the minimum and maximum element on it is
+ * 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;
+ }
+ ans += _pow(2, j - i);
+ ans %= MOD;
+ }
+ 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
+}