How to delete an element of array in efficient manner?

Question

pragma solidity ^0.4.24;
contract test{
    uint[] public array = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15];
    function removewithgap(uint index)  returns(uint[]) {
        if (index >= array.length) return;
        delete array[index];
        return array;
    }
    function removewithoutgap(uint index)  returns(uint[]) {
        if (index >= array.length) return;

        for (uint i = index; i<array.length-1; i++){
            array[i] = array[i+1];
        }
        delete array[array.length-1];
        array.length--;
        return array;
    }
}

When I am using removewithgap function my transaction cost is kind os normal. But when I use removewithoutgap function my transaction cost increases exponentially as the length of my array grows. Is there any efficent way to remove the element without gap?

Answer 1

Well, it's always costly when you want to perform the delete operation on an array in solidity. But I found a little bit more efficient manner to resolve this problem.

pragma solidity >=0.5.0 <0.7.0;
contract deletefromarray{
uint[] array;
mapping(uint=>uint) indexOfValue;

function removeWithoutGap(uint _valueToDelete) public {
    uint index = indexOfValue[_valueToDelete];
        if (index >= array.length) return;

        if (array.length > 1) {
        array[index] = array[array.length-1];
        }
        array.length--; 
    }
}

it just refunds gas setting non-zero storage values to zero again. It's a little cheaper than explicitly saying delete array[index]