_findHeightWiseOverlapsInCol(col) {
        let pushedGates = new Set();
        let h = 0;
        for (let row = 0; row < this.numWires; row++) {
            h -= 1;
            let gate = this.gateInSlot(col, row);
            if (gate !== undefined) {
                if (h > 0) {
                    pushedGates.add(row);
                }
                h = Math.max(h, gate.height);
            }
        }
        return pushedGates;
    }
@param {!int} col
@returns {!Set.<!int>}
@private