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+// 287. Find the Duplicate Number
+#include "leetcode.h"
+
+/* given an integer array 'nums' containing 'n + 1' integers where each integer
+ * is in the range '[1, n]' inclusive. there is only one repeated number in
+ * 'nums', return this repeated number. you must solve the problem without
+ * modifying the array 'nums' and uses only constant extra space.
+ */
+
+int findDuplicate(int *nums, int nums_size) {
+ int *cnt = (int *)calloc(nums_size, sizeof(int));
+ for (int i = 0; i < nums_size; i++)
+ cnt[nums[i] - 1]++;
+ for (int i = 0; i < nums_size; i++)
+ if (cnt[i] >= 2)
+ return i + 1;
+ free(cnt);
+ return -1;
+}
+
+int main() {
+ int n1[] = {1, 3, 4, 2, 2}, n2[] = {3, 1, 3, 4, 2};
+ printf("%d\n", findDuplicate(n1, 5)); // expect: 2
+ printf("%d\n", findDuplicate(n2, 5)); // expect: 3
+}