leetcode

commit f031d94a96ae6ea157da22dac6b7f533b18f5f9c
parent eaced75979196840bbb0138526d533515fa56720
Author: Jack Sangdahl <jack@pngu.org>
Date:   Sat, 26 Jul 2025 23:16:47 -0600

2210. count hills and valleys in an array

Diffstat:
A
count_hills_valleys_arr.c
 | 
31
+++++++++++++++++++++++++++++++
A
count_hills_valleys_arr.py
 | 
29
+++++++++++++++++++++++++++++

2 files changed, 60 insertions(+), 0 deletions(-)
diff --git a/count_hills_valleys_arr.c b/count_hills_valleys_arr.c
@@ -0,0 +1,31 @@
+// 2210. Count Hills and Valleys in an Array
+#include "leetcode.h"
+
+/*
+ * you are given a 0-indexed integer array 'nums'. an index 'i' is part of a
+ * hill in 'nums' if the closest non-equal neighbours of 'i' are smaller than
+ * 'nums[i]'. similarly, an index 'i' is part of a valley in 'nums' if the
+ * closest non-equal neighbours of 'i' are larger than 'nums[i]'. adjacent
+ * indices 'i' and 'j' are part of the same hill or valley if 'nums[i] ==
+ * nums[j]'. note that for an index to be part of a hill or valley, it must have
+ * a non-equal neighbour on both the left and right of the index. return the
+ * number of hills and valleys in 'nums'.
+ */
+
+int countHillValley(int *nums, int numsSize) {
+  int prev = 0, ans = 0;
+  for (int i = 1; i < numsSize - 1; ++i) {
+    if (nums[prev] == nums[i] || nums[i + 1] == nums[i])
+      continue;
+    if ((nums[prev] - nums[i] & INT_MIN) == (nums[i + 1] - nums[i] & INT_MIN))
+      ans++;
+    prev = i;
+  }
+  return ans;
+}
+
+int main() {
+  int n1[] = {2, 4, 1, 1, 6, 5}, n2[] = {6, 6, 5, 5, 4, 1};
+  printf("%d\n", countHillValley(n1, ARRAY_SIZE(n1))); // expect: 3
+  printf("%d\n", countHillValley(n2, ARRAY_SIZE(n2))); // expect: 0
+}
diff --git a/count_hills_valleys_arr.py b/count_hills_valleys_arr.py
@@ -0,0 +1,29 @@
+# 2210. Count Hills and Valleys in an Array
+from itertools import groupby
+
+"""
+you are given a 0-indexed integer array 'nums'. an index 'i' is part of a
+hill in 'nums' if the closest non-equal neighbours of 'i' are smaller than
+'nums[i]'. similarly, an index 'i' is part of a valley in 'nums' if the
+closest non-equal neighbours of 'i' are larger than 'nums[i]'. adjacent
+indices 'i' and 'j' are part of the same hill or valley if 'nums[i] ==
+nums[j]'. note that for an index to be part of a hill or valley, it must have
+a non-equal neighbour on both the left and right of the index. return the
+number of hills and valleys in 'nums'.
+"""
+
+
+class Solution(object):
+    def countHillValley(self, nums):
+        """
+        :type nums: List[int]
+        :rtype: int
+        """
+        a = [i for i, _ in groupby(nums)]
+        return sum(l > m < r or l < m > r for l, m, r in zip(a, a[1:], a[2:]))
+
+
+if __name__ == "__main__":
+    obj = Solution()
+    print(obj.countHillValley(nums=[2, 4, 1, 1, 6, 5]))
+    print(obj.countHillValley(nums=[6, 6, 5, 5, 4, 1]))