Leetcode 2149

Author: Kondareddy1209

Leetcode/Leetcode_2149.py

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+# LeetCode 2149. Rearrange Array Elements by Sign
+#
+# Problem Statement:
+# Given an array nums of even length consisting of an equal number of positive
+# and negative integers, rearrange the elements such that:
+#
+# 1. Every consecutive pair of integers has opposite signs.
+# 2. For all integers with the same sign, their relative order is preserved.
+# 3. The rearranged array begins with a positive integer.
+#
+# Return the modified array.
+#
+# Example:
+# Input:  nums = [3,1,-2,-5,2,-4]
+# Output: [3,-2,1,-5,2,-4]
+#
+# Approach:
+# - Create a result array of the same size as nums.
+# - Use two pointers:
+#     pos = 0 -> stores the next available even index for positive numbers.
+#     neg = 1 -> stores the next available odd index for negative numbers.
+# - Traverse the input array once:
+#     * If the current number is positive, place it at index 'pos'
+#       and move pos by 2.
+#     * If the current number is negative, place it at index 'neg'
+#       and move neg by 2.
+# - This preserves the relative ordering of positive and negative numbers
+#   while ensuring alternating signs.
+#
+# Time Complexity: O(n)
+# - Each element is visited exactly once.
+#
+# Space Complexity: O(n)
+# - An additional array of size n is used to store the result.
+
+from typing import List
+
+class Solution:
+    def rearrangeArray(self, nums: List[int]) -> List[int]:
+        n = len(nums)
+
+        # Even indices for positive numbers
+        pos = 0
+
+        # Odd indices for negative numbers
+        neg = 1
+
+        # Result array
+        temp = [0] * n
+
+        for i in range(n):
+            if nums[i] > 0:
+                temp[pos] = nums[i]
+                pos += 2
+            else:
+                temp[neg] = nums[i]
+                neg += 2
+
+        return temp