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Pivot Index

Certification: Basic Level Accuracy: 0% Submissions: 4 Points: 5

Write a Java program to find the pivot index of an 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 right of the index. If such an index does not exist, return -1. If there are multiple pivot indexes, return the leftmost pivot index.

Example 1
     
  • Input: nums = [1, 7, 3, 6, 5, 6]
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  • Output: 3
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  • Explanation: 
       
    • Step 1: Calculate the total sum of all elements in the array: 1 + 7 + 3 + 6 + 5 + 6 = 28.
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    • Step 2: Initialize leftSum = 0 and rightSum = totalSum - nums[0] = 28 - 1 = 27.
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    • Step 3: For index 0: leftSum = 0, rightSum = 27, not equal, so not a pivot index.
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    • Step 4: For index 1: leftSum = 1, rightSum = 27 - 7 = 20, not equal, so not a pivot index.
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    • Step 5: For index 2: leftSum = 1 + 7 = 8, rightSum = 20 - 3 = 17, not equal, so not a pivot index.
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    • Step 6: For index 3: leftSum = 8 + 3 = 11, rightSum = 17 - 6 = 11, which are equal, so index 3 is the pivot index.
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    •
Example 2
     
  • Input: nums = [1, 2, 3]
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  • Output: -1
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  • Explanation: 
       
    • Step 1: Calculate the total sum of all elements in the array: 1 + 2 + 3 = 6.
      •  
    • Step 2: Initialize leftSum = 0 and rightSum = totalSum - nums[0] = 6 - 1 = 5.
      •  
    • Step 3: For index 0: leftSum = 0, rightSum = 5, not equal, so not a pivot index.
      •  
    • Step 4: For index 1: leftSum = 1, rightSum = 5 - 2 = 3, not equal, so not a pivot index.
      •  
    • Step 5: For index 2: leftSum = 1 + 2 = 3, rightSum = 3 - 3 = 0, not equal, so not a pivot index.
      •  
    • Step 6: No pivot index found, so return -1.
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    •
Constraints
     
  • 1 ≤ nums.length ≤ 10^4
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  • -1000 ≤ nums[i] ≤ 1000
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  • Time Complexity: O(n)
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  • Space Complexity: O(1)
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ArraysNumberHCL TechnologiesZomato
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Hint
Solution

Solution Hints

    
  
  • Calculate the total sum of the array
    • 
  
  • Iterate through the array while keeping track of the sum of elements to the left of the current index
    • 
  
  • For each index, calculate the sum to the right by subtracting the left sum and the current element from the total sum
    • 
  
  • If the left sum equals the right sum, return the current index as the pivot index
    • 
  
  • If no pivot index is found after iterating through the array, return -1
    •

Steps to solve by this approach:

 Step 1: Calculate the total sum of all elements in the array.
 Step 2: Initialize a variable leftSum to 0 to track the sum of elements to the left of the current index.
 Step 3: Iterate through each element of the array.
 Step 4: At each index, calculate the sum of elements to the right using: rightSum = totalSum - leftSum - currentElement.
 Step 5: Check if leftSum equals rightSum. If they are equal, return the current index as the pivot index.
 Step 6: Before moving to the next element, add the current element to leftSum.
 Step 7: If no pivot index is found after iterating through the entire array, return -1.

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