席位分配-最大余数法

getPercentWithPrecision.js

/**
 * 议会席位分配
 * echarts source code: https://github.com/apache/echarts/commit/fa8db37e5e11b74cbe6e377399c1bb49b8847704
 * echarts issues: https://github.com/apache/echarts/issues/5850
 * Ovilia fix: http://zhangwenli.com/blog/2017/06/13/pie-percentage
 * wiki 最大余数法: https://en.wikipedia.org/wiki/Largest_remainder_method
 */
function getPercentWithPrecision(valueList = [], idx, precision) {
    var sum = valueList.reduce((acc, val) => acc + val, 0)
    if (sum === 0) return 0
    var digits = Math.pow(10, precision)
    var votesPerQuota = valueList.map((value) => value / sum * digits * 100)
    var targetSeats = digits * 100;
    var seats = votesPerQuota.map((votes) => Math.floor(votes))
    var currentSum = seats.reduce((acc, val) => acc + val, 0)
    var remainder = votesPerQuota.map((votes, idx) => votes - seats[idx])

    while (currentSum < targetSeats) {
        // Find next largest remainder.
        var max = Number.NEGATIVE_INFINITY
        var maxId = null
        for (var i = 0, len = remainder.length; i < len; ++i) {
            if (remainder[i] > max) {
                max = remainder[i]
                maxId = i;
            }
        }

        // Add a vote to max remainder.
        ++seats[maxId]
        remainder[maxId] = 0
        ++currentSum
    }

    return seats[idx] / digits
}

getPercentWithPrecision.test.js

getPercentWithPrecision([50.5, 49.5], 0, 0) === 51;
getPercentWithPrecision([50.5, 49.5], 1, 0) === 49;
getPercentWithPrecision([12.34, 34.56, 53.1], 0, 1) === 12.3;
getPercentWithPrecision([12.34, 34.56, 53.1], 1, 1) === 34.6;
getPercentWithPrecision([12.34, 34.56, 53.1], 2, 1) === 53.1;
getPercentWithPrecision([1.678, 4.783, 2.664, 0.875], 0, 0) === 17;
getPercentWithPrecision([1.678, 4.783, 2.664, 0.875], 1, 0) === 48;
getPercentWithPrecision([1.678, 4.783, 2.664, 0.875], 2, 0) === 26;
getPercentWithPrecision([1.678, 4.783, 2.664, 0.875], 3, 0) === 9;