diff --git a/data_structures/arrays/maximum_subarray.rb b/data_structures/arrays/maximum_subarray.rb index ad2059e..b1f7164 100644 --- a/data_structures/arrays/maximum_subarray.rb +++ b/data_structures/arrays/maximum_subarray.rb @@ -1,56 +1,66 @@ -#Given an integer array nums, find the contiguous subarray (containing at least one number) which has the largest sum and return its sum. -#A subarray is a contiguous part of an array. +# Given an integer array nums, find the contiguous subarray (containing at least one number) which has the largest sum and return its sum. +# A subarray is a contiguous part of an array. -#Example 1: -#Input: nums = [-2,1,-3,4,-1,2,1,-5,4] -#Output: 6 -#Explanation: [4,-1,2,1] has the largest sum = 6. +# Example 1: +# Input: nums = [-2,1,-3,4,-1,2,1,-5,4] +# Output: 6 +# Explanation: [4,-1,2,1] has the largest sum = 6. -#Example 2: -#Input: nums = [1] -#Output: 1 +# Example 2: +# Input: nums = [1] +# Output: 1 -#Example 3: -#Input: nums = [5,4,-1,7,8] -#Output: 23 +# Example 3: +# Input: nums = [5,4,-1,7,8] +# Output: 23 -#Constraints: -#1 <= nums.length <= 3 * 104 -#-105 <= nums[i] <= 105 - - - - -#Dynamic Programming Approach (Kadane's Algorithm) - O(n) Time / O(1) Space -#Init max_sum as first element -#Return first element if the array length is 1 -#Init current_sum as 0 -#Iterate through the array: -#if current_sum < 0, then reset it to 0 (to eliminate any negative prefixes) -#current_sum += num -#max_sum = current_sum if current_sum is greater than max_sum -#Return max_sum +# Constraints: +# 1 <= nums.length <= 3 * 104 +# -105 <= nums[i] <= 105 +# Dynamic Programming Approach (Kadane's Algorithm) - O(n) Time / O(1) Space +# +# Init max_sum as first element +# Return first element if the array length is 1 +# Init current_sum as 0 +# Iterate through the array: +# if current_sum < 0, then reset it to 0 (to eliminate any negative prefixes) +# current_sum += num +# max_sum = current_sum if current_sum is greater than max_sum +# Return max_sum # @param {Integer[]} nums # @return {Integer} def max_sub_array(nums) - #initialize max sum to first number - max_sum = nums[0] - - #return first number if array length is 1 - return max_sum if nums.length == 1 - - #init current sum to 0 - current_sum = 0 - - #iterate through array, reset current_sum to 0 if it ever goes below 0, track max_sum with highest current_sum - nums.each do |num| - current_sum = 0 if current_sum < 0 - current_sum += num - max_sum = [max_sum, current_sum].max - end - - #return answer - max_sum + # initialize max sum to first number + max_sum = nums[0] + + # return first number if array length is 1 + return max_sum if nums.length == 1 + + # init current sum to 0 + current_sum = 0 + + # iterate through array, reset current_sum to 0 if it ever goes below 0, track max_sum with highest current_sum + nums.each do |num| + current_sum = 0 if current_sum < 0 + + current_sum += num + + max_sum = [max_sum, current_sum].max + end + + max_sum end + +nums = [-2, 1, -3, 4, -1, 2, 1, -5, 4] +print max_sub_array(nums) +# Output: 6 + +nums = [1] +print max_sub_array(nums) +# Output: 1 + +nums = [5, 4, -1, 7, 8] +print max_sub_array(nums) +# Output: 23