public class RedOrBlack {
    def static final BLACK = 0
    def static final RED = 1
    def static final ZERO = 2

    def m_rng = new Random()

    def spinWheel() {
        // Value range: [0..36].
        def value = m_rng.nextInt(37)
        if (value == 0) {
            return ZERO
        } else if (value % 2 == 0) {
            return BLACK
        } 
        return RED
    }

    def runSimulation(spinsLeft) {
        // 'withDefault' ensures that lookups with non-existent keys return a value of '0'.
        def seriesMapBlack = [:].withDefault { 0 }
        def seriesMapRed = [:].withDefault { 0 }
        def seriesMapZero = [:].withDefault { 0 }
        def seriesMaps = [seriesMapBlack, seriesMapRed, seriesMapZero]

        def prevColor
        def currentSeriesLength
        def initialized = false

        while (spinsLeft-- > 0) {
            def newColor = spinWheel()

            // Initialize upon first spin.
            if (!initialized) {
                prevColor = newColor
                currentSeriesLength = 0
                initialized = true
            }

            // Current series continues.
            if (newColor == prevColor) {
                ++currentSeriesLength;
            // New color, series terminated.
            } else {
                // Keep track of how often a particular series length (of previous color) occurred.
                ++seriesMaps[prevColor][currentSeriesLength];
                // Current series is over.
                currentSeriesLength = 0 
            }

            // Ensure that the final series is entered as well.
            if (spinsLeft == 0) {
                ++seriesMaps[newColor][currentSeriesLength]
            }

            prevColor = newColor
        }

        return seriesMaps
    }
}