View and pure functions in Blockchain / Solidity - Time & Space Complexity

Time Complexity: View and pure functions

O(n)

Understanding Time Complexity

When working with blockchain smart contracts, view and pure functions let us read data without changing it.

We want to understand how the time to run these functions grows as the input size grows.

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

contract Example {
    uint[] numbers;

    function getSum() public view returns (uint) {
        uint sum = 0;
        for (uint i = 0; i < numbers.length; i++) {
            sum += numbers[i];
        }
        return sum;
    }

    function getConstant() public pure returns (uint) {
        return 42;
    }
}
    

This contract has a view function that sums all numbers in an array and a pure function that returns a fixed number.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: The for-loop in getSum() that goes through each number in the array.
• How many times: Once for each element in the numbers array.
• Pure function: getConstant() does not repeat any operation; it just returns a fixed value.

How Execution Grows With Input

As the array size grows, the number of steps to sum all elements grows too.

Input Size (n)	Approx. Operations
10	10 additions
100	100 additions
1000	1000 additions

Pattern observation: The work grows directly with the number of items; double the items, double the work.

Final Time Complexity

Time Complexity: O(n)

This means the time to run the view function grows linearly with the input size.

Common Mistake

[X] Wrong: "View and pure functions always run instantly no matter the input size."

[OK] Correct: While pure functions with fixed work run quickly, view functions that loop over data take longer as data grows.

Interview Connect

Understanding how reading data scales helps you write efficient smart contracts and answer questions about cost and speed.

Self-Check

"What if the getSum() function used recursion instead of a loop? How would the time complexity change?"

Practice

1. Which statement best describes a view function in a blockchain smart contract?

easy

A. It reads blockchain data but does not modify it.

B. It modifies blockchain data and stores new values.

C. It neither reads nor writes blockchain data.

D. It only accepts inputs and returns no output.

Solution

1. Step 1: Understand the role of view functions

   View functions are designed to read data from the blockchain without changing it.

2. Step 2: Compare options with definition

   It reads blockchain data but does not modify it. matches this definition exactly, while others describe modifying or ignoring blockchain data.

3. Final Answer:

   It reads blockchain data but does not modify it. -> Option A

4. Quick Check:

   View function = reads only [OK]

Hint: View functions read data but never change it [OK]

Common Mistakes:

• Confusing view with functions that modify data
• Thinking view functions can write data
• Assuming view functions do not read blockchain data

2. Which of the following is the correct syntax to declare a pure function in Solidity?

easy

A. function calculate() public pure returns (uint) {}

B. function calculate() public view returns (uint) {}

C. function calculate() public returns (uint) {}

D. function calculate() pure returns (uint) {}

Solution

1. Step 1: Recall Solidity function declaration syntax

   Functions must specify visibility (e.g., public) and state mutability (pure/view) before returns.

2. Step 2: Identify correct pure function syntax

   function calculate() public pure returns (uint) {} correctly includes visibility and pure keyword before returns. function calculate() pure returns (uint) {} misses visibility, which is required.

3. Final Answer:

   function calculate() public pure returns (uint) {} -> Option A

4. Quick Check:

   Pure function syntax = public pure returns [OK]

Hint: Pure functions need visibility and 'pure' keyword before returns [OK]

Common Mistakes:

• Omitting visibility keyword
• Using view instead of pure
• Placing pure after returns

3. What will be the output of this Solidity function call?

function multiply(uint a, uint b) public pure returns (uint) {
    return a * b;
}

// Called with multiply(3, 4)

medium

A. Error: function cannot modify state

B. 7

C. 0

D. 12

Solution

1. Step 1: Understand the function logic

   The function multiplies two unsigned integers and returns the result.

2. Step 2: Calculate the output for inputs 3 and 4

   3 multiplied by 4 equals 12, so the function returns 12.

3. Final Answer:

   12 -> Option D

4. Quick Check:

   3 * 4 = 12 [OK]

Hint: Multiply inputs directly in pure function for output [OK]

Common Mistakes:

• Adding instead of multiplying
• Expecting state change error
• Confusing pure with view function behavior

4. Identify the error in this Solidity function declared as view:

uint count = 0;
function increment() public view returns (uint) {
    count += 1;
    return count;
}

medium

A. Missing returns keyword.

B. Cannot modify state variable in a view function.

C. Function should be pure, not view.

D. No error, code is correct.

Solution

1. Step 1: Understand view function restrictions

   View functions cannot modify state variables; they only read data.

2. Step 2: Analyze the code behavior

   The function increments a state variable, which is a write operation, causing an error.

3. Final Answer:

   Cannot modify state variable in a view function. -> Option B

4. Quick Check:

   View functions = no state changes [OK]

Hint: View functions cannot change state variables [OK]

Common Mistakes:

• Thinking view allows state changes
• Confusing pure and view keywords
• Ignoring state variable modification

5. You want to create a function that calculates the sum of two numbers without reading or modifying any blockchain data. Which function type should you use and how should it be declared in Solidity?

hard

A. Use a view function declared as function sum(uint a, uint b) public view returns (uint).

B. Use a regular function declared as function sum(uint a, uint b) public returns (uint).

C. Use a pure function declared as function sum(uint a, uint b) public pure returns (uint).

D. Use a payable function declared as function sum(uint a, uint b) public payable returns (uint).

Solution

1. Step 1: Identify function requirements

   The function must not read or modify blockchain data, only use inputs to calculate sum.

2. Step 2: Choose correct function type and declaration

   Pure functions do not read or write blockchain data, so declaring it as public pure with inputs and returns is correct.

3. Final Answer:

   Use a pure function declared as function sum(uint a, uint b) public pure returns (uint). -> Option C

4. Quick Check:

   Pure = no blockchain data access [OK]

Hint: Pure functions only use inputs, no blockchain data access [OK]

Common Mistakes:

• Using view instead of pure
• Using payable unnecessarily
• Not specifying pure keyword