724, 1480

README.md

@@ -58,6 +58,7 @@
 | 605 | Design Circular Queue | [Ruby](./algorithms/ruby/0605-can-place-flowers.rb) | Easy |
 | 622 | Design Circular Queue | [Ruby](./algorithms/ruby/0622-design-circular-queue.rb) | Medium |
 | 652 | Find Duplicate Subtrees | [Ruby](./algorithms/ruby/0652-find-duplicate-subtrees.rb) | Medium |
+| 724 | Find Pivot Index | [Ruby](./algorithms/ruby/0724-find-pivot-index.rb) | Easy |
 | 733 | Flood Fill | [Ruby](./algorithms/ruby/0733-flood-fill.rb) | Easy |
 | 783 | Minimum Distance Between BST Nodes | [Ruby](./algorithms/ruby/0783-minimum-distance-between-bst-nodes.rb) [Python3](./algorithms/python3/0783-minimum-distance-between-bst-nodes.py) | Easy |
 | 875 | Koko Eating Bananas | [Ruby](./algorithms/ruby/0875-koko-eating-bananas.rb) [Python3](./algorithms/python3/0875-koko-eating-bananas.py) | Medium |
@@ -76,6 +77,7 @@
 | 1345 | Jump Game IV | [Ruby](./algorithms/ruby/1345-jump-game-iv.rb) | Hard |
 | 1470 | Shuffle the Array | [Ruby](./algorithms/ruby/1470-shuffle-the-array.rb) | Easy |
 | 1472 | Design Browser History | [Ruby](./algorithms/ruby/1472-design-browser-history.rb) | Medium |
+| 1480 | Running Sum of 1d Array | [Ruby](./algorithms/ruby/1480-running-sum-of-1d-array.rb) | Easy |
 | 1523 | Count Odd Numbers in an Interval Range | [Ruby](./algorithms/ruby/1523-count-odd-numbers-in-an-interval-range.rb) | Easy |
 | 1539 | Kth Missing Positive Number | [Ruby](./algorithms/ruby/1539-kth-missing-positive-number.rb) | Easy |
 | 1675 | Minimize Deviation in Array | [Ruby](./algorithms/ruby/1675-minimize-deviation-in-array.rb) | Hard |

algorithms/ruby/0724-find-pivot-index.rb

@@ -0,0 +1,72 @@
+# frozen_string_literal: true
+
+# 724. Find Pivot Index
+# https://leetcode.com/problems/find-pivot-index
+
+=begin
+
+Given an array of integers nums, calculate the pivot index of this array.
+
+The pivot index is the index where the sum of all the numbers strictly to the left of the index is equal to the sum of all the numbers strictly to the index's right.
+
+If the index is on the left edge of the array, then the left sum is 0 because there are no elements to the left. This also applies to the right edge of the array.
+
+Return the leftmost pivot index. If no such index exists, return -1
+
+### Example 1:
+Input: nums = [1,7,3,6,5,6]
+Output: 3
+Explanation:
+The pivot index is 3.
+Left sum = nums[0] + nums[1] + nums[2] = 1 + 7 + 3 = 11
+Right sum = nums[4] + nums[5] = 5 + 6 = 11
+
+### Example 2:
+Input: nums = [1,2,3]
+Output: -1
+Explanation:
+There is no index that satisfies the conditions in the problem statement.
+
+### Example 3:
+Input: nums = [2,1,-1]
+Output: 0
+Explanation:
+The pivot index is 0.
+Left sum = 0 (no elements to the left of index 0)
+Right sum = nums[1] + nums[2] = 1 + -1 = 0
+
+### Constraints:
+* 1 <= nums.length <= 104
+* -1000 <= nums[i] <= 1000
+
+=end
+
+# Runtime 109 ms
+# Memory 212.6 MB
+# @param {Integer[]} nums
+# @return {Integer}
+def pivot_index(nums)
+  sum = nums.sum
+  left_sum = 0
+
+  nums.each_with_index do |num, index|
+    return index if left_sum == sum - left_sum - num
+
+    left_sum += num
+  end
+
+  -1
+end
+
+# **************** #
+#       TEST       #
+# **************** #
+
+require "test/unit"
+class Test_pivot_index < Test::Unit::TestCase
+  def test_
+    assert_equal 3, pivot_index([1, 7, 3, 6, 5, 6])
+    assert_equal(-1, pivot_index([1, 2, 3]))
+    assert_equal 0, pivot_index([2, 1, -1])
+  end
+end

algorithms/ruby/1480-running-sum-of-1d-array.rb

@@ -0,0 +1,51 @@
+# frozen_string_literal: true
+
+# 1480. Running Sum of 1d Array
+# https://leetcode.com/problems/running-sum-of-1d-array
+
+=begin
+
+Given an array nums. We define a running sum of an array as runningSum[i] = sum(nums[0]…nums[i]).
+
+Return the running sum of nums.
+
+### Example 1:
+Input: nums = [1,2,3,4]
+Output: [1,3,6,10]
+Explanation: Running sum is obtained as follows: [1, 1+2, 1+2+3, 1+2+3+4].
+
+### Example 2:
+Input: nums = [1,1,1,1,1]
+Output: [1,2,3,4,5]
+Explanation: Running sum is obtained as follows: [1, 1+1, 1+1+1, 1+1+1+1, 1+1+1+1+1].
+
+### Example 3:
+Input: nums = [3,1,2,10,1]
+Output: [3,4,6,16,17]
+
+### Constraints:
+
+* 1 <= nums.length <= 1000
+* -10^6 <= nums[i] <= 10^6
+=end
+
+# Runtime 96 ms
+# Memory 211.1 MB
+# @param {Integer[]} nums
+# @return {Integer[]}
+def running_sum(nums)
+  nums.reduce([]) { _1 << _2 + (_1.last || 0) }
+end
+
+# **************** #
+#       TEST       #
+# **************** #
+
+require "test/unit"
+class Test_running_sum < Test::Unit::TestCase
+  def test_
+    assert_equal [1, 3, 6, 10], running_sum([1, 2, 3, 4])
+    assert_equal [1, 2, 3, 4, 5], running_sum([1, 1, 1, 1, 1])
+    assert_equal [3, 4, 6, 16, 17], running_sum([3, 1, 2, 10, 1])
+  end
+end