FIndPivotIndex.go

/*
Given an array of integers nums, write a method that returns the "pivot" index of this array.

We define the pivot index as the index where the sum of all the numbers to the left of the index is equal to the sum of all the numbers to the right of the index.

If no such index exists, we should return -1. If there are multiple pivot indexes, you should return the left-most pivot index.

 

Example 1:

Input: nums = [1,7,3,6,5,6]
Output: 3
Explanation:
The sum of the numbers to the left of index 3 (nums[3] = 6) is equal to the sum of numbers to the right of index 3.
Also, 3 is the first index where this occurs.
Example 2:

Input: nums = [1,2,3]
Output: -1
Explanation:
There is no index that satisfies the conditions in the problem statement.
 

Constraints:

The length of nums will be in the range [0, 10000].
Each element nums[i] will be an integer in the range [-1000, 1000].
*/

package main

import (
	"log"
)

func main() {
	tests := [][]int{{1,7,3,6,5,6}, {1,2,3}, {-1,-1,-1,0,1,1}}
	for _, test := range tests {
		log.Printf("pivotIndex(%v) == %d\n", test, pivotIndex2(test))
	}
}

func pivotIndex2(nums []int) int {
	// if the total of all elements in th array is X, and the total of all elements upto an index i is y,
	// then the total of elemnts to the right of i is X-arr[i]-y


	// calculate the total of all elements in the collection
	fullTotal := 0
	for _, n := range nums {
		fullTotal += n
	}

	// keep running total of all elements to the left of nums[i]
	leftTotal := 0
	for i := 0; i < len(nums); i++ {
		rightTotal := fullTotal - nums[i] - leftTotal

		if rightTotal == leftTotal {
			return i
		} else {
			// update left total
			leftTotal += nums[i]
		}
	}

	// no idex with same element total to the left and to the right found in nums
	return -1
}

func pivotIndex(nums []int) int {
		// totals from left
		totalsLeft := []int{}

		total := 0
		for i := 0; i < len(nums); i++ {
			total += nums[i]
			totalsLeft = append(totalsLeft, total)
		}

		log.Printf("pivotIndex(): totalsLeft: %v\n", totalsLeft)

		// totals from right
		totalsRight := []int{}

		total = 0
		for i := len(nums)-1; i >= 0; i-- {
			total += nums[i]
			totalsRight = append(totalsRight, total)
		}

		log.Printf("pivotIndex(): totalsRight: %v\n", totalsRight)

		for i := 0; i < len(totalsLeft); i++ {
			leftTot := 0
			if i-1 >= 0 {
				leftTot = totalsLeft[i-1]

				rightTot := 0
				
				if (len(totalsRight)-(i+2)) >= 0 {
					rightTot = totalsRight[len(totalsRight)-(i+2)]

					if leftTot == rightTot {
						return i
					}		
				}	
			}

			// rightTot := 0
			// if i+1 < len(totalsRight) {
			// 	rightTot = totalsRight[i+1]
			// }

			// if (len(totalsRight)-(i+2)) >= 0 {
			// 	rightTot = totalsRight[len(totalsRight)-(i+2)]
			// }

			// if leftTot == rightTot {
			// 	return i
			// }
		}

		return -1
}