Add solution for pivot index

Author: kwnna15

Diff for: prefix-sum/pivot-index/README.md

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+# 1732. Find the Highest Altitude
+
+## Description
+See https://leetcode.com/problems/find-the-highest-altitude/description/
+
+## Problem
+There is a biker going on a road trip. The road trip consists of `n + 1` points at different altitudes. The biker starts his trip on point `0` with altitude equal `0`.
+
+You are given an integer array `gain` of length `n` where `gain[i]` is the net gain in altitude between points `i`​​​​​​ and `i + 1` for all `(0 <= i < n)`. Return the highest altitude of a point.
+
+## Example 1
+
+```
+Input: gain = [-5,1,5,0,-7]
+Output: 1
+Explanation: The altitudes are [0,-5,-4,1,1,-6]. The highest is 1.
+```
+
+## Example 2
+
+```
+Input: gain = [-4,-3,-2,-1,4,3,2]
+Output: 0
+Explanation: The altitudes are [0,-4,-7,-9,-10,-6,-3,-1]. The highest is 0.
+```
+
+## Constraints
+
+```
+n == gain.length
+1 <= n <= 100
+-100 <= gain[i] <= 100
+```

Diff for: prefix-sum/pivot-index/pivot.py

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+def index(nums: list[int]) -> int:
+    left, right = 0, sum(nums)
+    for idx, ele in enumerate(nums):
+        right -= ele
+        if left == right:
+            return idx
+        left += ele
+    return -1

Diff for: prefix-sum/pivot-index/pivot_test.py

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+from pivot import index
+
+def test_example_1():
+    nums = [1, 7, 3, 6, 5, 6]
+    assert index(nums) == 3
+
+def test_example_2():
+    nums = [1, 2, 3]
+    assert index(nums) == -1
+
+def test_example_3():
+    nums = [2, 1, -1]
+    assert index(nums) == 0
+
+def test_example_4():
+    nums = [0, 0, 0, 0, 1]
+    assert index(nums) == 4
+
+def test_example_6():
+    nums = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
+    assert index(nums) == -1