年龄排序

func sortAges(_ ages: inout [Int]) {
    guard !ages.isEmpty else { return }
    
    let oldestAge: Int = 99
    var timesOfAge = [Int]() // 统计每个年龄出现的次数
    
    // 年龄允许的范围是 0~99
    guard ages.allSatisfy({ $0 > 0}),
          ages.allSatisfy({ $0 <= oldestAge})
    else { return }
    
    for _ in 0...oldestAge {
        timesOfAge.append(0)
    }
    
    for i in 0..<ages.count {
        let age = ages[i]
        timesOfAge[age] += 1
    }
    
    var index = 0
    for i in 0...oldestAge {
        for _ in 0..<timesOfAge[i] {
            ages[index] = i
            index += 1
        }
    }
}

摘抄资料：《剑指offer》