How to check if one value exists in an array?

user_16462963 0
Viewed 2519

I need to check if all the values in X array exist in Y array do something. The order does not matter.

contract test {

    uint[] numbers1;
    uint[] numbers2;

    function push1(uint num1, uint num2, uint num3) public {
        numbers1.push(num1);
        numbers1.push(num2);
        numbers1.push(num3);
    }

    function push2(uint num1, uint num2, uint num3) public {
        numbers2.push(num1);
        numbers2.push(num2);
        numbers2.push(num3);
    }

}

How can I check all numbers in numbers1 exist in numbers2 or not?

solidity
1 Answers

There are two approaches.

You can create a view function (docs) that loops through the array and returns true if the item is found. Mind that a view function can be invoked using a gas-free read-only call instead of a (read-write) transaction costing gas fees.

function exists1(uint num) public view returns (bool) {
    for (uint i = 0; i < numbers1.length; i++) {
        if (numbers1[i] == num) {
            return true;
        }
    }

    return false;
}

This approach has a linear complexity. So if you need to validate the value existence during a transaction, it might be costly depending on the total amount of items in the array.

So there's a second approach - duplicate the values as keys of a mapping (docs) that can be accessed directly through its key. There's a constant complexity to search the value but it costs double to store the value.

uint[] numbers1;
mapping(uint => bool) public exists1; // default value for each key is false

function push1(uint num1, uint num2, uint num3) public {
    numbers1.push(num1);
    numbers1.push(num2);
    numbers1.push(num3);

    exists1[num1] = true;
    exists1[num2] = true;
    exists1[num3] = true;
}
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