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-rw-r--r--number_subarr_odd_sum.c24
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diff --git a/number_subarr_odd_sum.c b/number_subarr_odd_sum.c
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+// 1524. Number of Sub-arrays With Odd Sum
+#include "leetcode.h"
+
+/*
+ * given an array of integers 'arr', return the number of subarrays with an odd
+ * sum. since the answer can be very large, return it modulo 10e9+7.
+ */
+
+int numOfSubarrays(int *arr, int arrSize) {
+ int curr = 0, ans = 0, cnt[] = {1, 0}, mod = 1e9 + 7;
+ for (int i = 0; i < arrSize; i++) {
+ curr ^= arr[i] & 1;
+ ans = (ans + cnt[1 - curr]) % mod;
+ cnt[curr]++;
+ }
+ return ans;
+}
+
+int main() {
+ int a1[] = {1, 3, 5}, a2[] = {2, 4, 6}, a3[] = {1, 2, 3, 4, 5, 6, 7};
+ printf("%d\n", numOfSubarrays(a1, ARRAY_SIZE(a1))); // expect: 4
+ printf("%d\n", numOfSubarrays(a2, ARRAY_SIZE(a2))); // expect: 0
+ printf("%d\n", numOfSubarrays(a3, ARRAY_SIZE(a3))); // expect: 16
+}