[白俊]2170号:スクライブ

var answer = 0

fun main() {
    val br = System.`in`.bufferedReader()
    val bw = System.out.bufferedWriter()

    val n = br.readLine().toInt()

    val lines = mutableListOf<Pair<Int, Int>>()
    for (i in 0 until n) {
        val (x, y) = br.readLine().split(" ").map { it.toInt() }
        lines.add(Pair(x, y))
    }
    lines.sortBy { it.first }
    val answer = lineSweepingStartWithOne(lines)
    bw.write("$answer")

    br.close()
    bw.close()
}

fun lineSweepingStartWithOne(lines: MutableList<Pair<Int, Int>>): Int {
    var start = lines[0].first
    var end = lines[0].second
    lines.drop(1).forEach { (x, y) ->
        if (isSeparateLine(x, end)) {
            accumulateLength(end - start)
            // new start position
            start = x
            end = y
        } else if (isLongerLine(y, end)) end = y
    }
    accumulateLength(end - start)
    return answer
}

fun isSeparateLine(x: Int, end: Int): Boolean {
    return x > end
}

fun accumulateLength(length: Int) {
    answer += length
}

fun isLongerLine(y: Int, end: Int): Boolean {
    return y > end
}

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