// Сложение ступенчатых графиков

struct Point {
    var time: Int
    var value: Int
}

func sumSeries(a: [Point], b: [Point]) -> [Point] {
    var result: [Point] = []
    var pntA = 0
    var pntB = 0
    var last_a = 0
    var last_b = 0

    while pntA < a.count && pntB < b.count {
        if a[pntA].time < b[pntB].time {
            result.append(Point(time: a[pntA].time, value: a[pntA].value + last_b))
            last_a = a[pntA].value
            pntA += 1
        } else if a[pntA].time == b[pntB].time {
            result.append(Point(time: a[pntA].time, value: a[pntA].value + b[pntB].value))
            last_a = a[pntA].value
            last_b = b[pntB].value
            pntA += 1
            pntB += 1
        } else {
            result.append(Point(time: b[pntB].time, value: b[pntB].value + last_a))
            last_b = b[pntB].value
            pntB += 1
        }
    }

    while pntA < a.count {
        result.append(Point(time: a[pntA].time, value: a[pntA].value + last_b))
        pntB += 1
    }

    while pntB < b.count {
        result.append(Point(time: b[pntB].time, value: b[pntB].value + last_a))
        pntB += 1
    }

    return result
}

var result = sumSeries(a: [Point(time: 1, value: 2), Point(time: 5, value: 1)], b: [Point(time: 2, value: 4), Point(time: 3, value: 6), Point(time: 9, value: 7)])
for point in result {
    print("{\(point.time), \(point.value)}", terminator: " ")
}