[Alikberov]

let so = ['O', 'S', 'O', 'S', 'O', 'S', 'O', 'O', 'S', 'O', 'S', 'S', 'O', 'S', 'O', 'O' ];
    let soi = [];

so.reduce(
    function(prev, current, index, arr) {
        if(prev == current)
            soi.push([current, index - 1, index]);
        return current;
    }
);
console.log(soi);