[рони]

const dt = [
    [1, 2],
    [1, 3],
    [2, 4],
    [2, 3]
]
let arr = dt.flat();
let min = Math.min(...arr);
let max = Math.max(...arr);

let t = 0;
for (let i = min; i <= max; i++) {
	let c = 0;
	dt.forEach(el => {
		if ((el[0] <= i) && (i < el[1])) ++c
	})
	alert(i + ' - ' + c)
	t = Math.max(t, c)
}
alert(t)

const dt = [
            [1, 2],
            [1, 3],
            [2, 4],
            [2, 3]
        ]
        let arr = dt.map(([a, b]) => Array.from({
            length: b - a
        }, (_, i) => a + i)).flat().sort((a, b) => a - b);

        let c = 0,
            t = 0,
            n;
        for (let i of arr) {
            if (i === n) c++;
            else {
                c = 1;
                n = i;
            }
            if (c > t) t = c;

        }

        alert(t)