[Swift]LeetCode1093. 大样本统计 | Statistics from a Large Sample

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We sampled integers between 0 and 255, and stored the results in an array count:  count[k] is the number of integers we sampled equal to k.

Return the minimum, maximum, mean, median, and mode of the sample respectively, as an array of floating point numbers.  The mode is guaranteed to be unique.

(Recall that the median of a sample is:

• The middle element, if the elements of the sample were sorted and the number of elements is odd;
• The average of the middle two elements, if the elements of the sample were sorted and the number of elements is even.)

Example 1:

Input: count = [0,1,3,4,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]
Output: [1.00000,3.00000,2.37500,2.50000,3.00000]

Example 2:

Input: count = [0,4,3,2,2,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]
Output: [1.00000,4.00000,2.18182,2.00000,1.00000]

Constraints:

1. count.length == 256
2. 1 <= sum(count) <= 10^9
3. The mode of the sample that count represents is unique.
4. Answers within 10^-5 of the true value will be accepted as correct.

---

我们对 0 到 255 之间的整数进行采样，并将结果存储在数组 count 中：count[k] 意味着采样的整数为 k。

我们以 浮点数 数组的形式，分别返回样本的最小值、最大值、平均值、中位数和众数。其中，众数是保证唯一的。

我们先来回顾一下中位数的知识：

• 如果样本中的元素有序，并且元素数量为奇数时，中位数为最中间的那个元素；
• 如果样本中的元素有序，并且元素数量为偶数时，中位数为中间的两个元素的平均值。

示例 1：

输入：count = [0,1,3,4,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]
输出：[1.00000,3.00000,2.37500,2.50000,3.00000]

示例 2：

输入：count = [0,4,3,2,2,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]
输出：[1.00000,4.00000,2.18182,2.00000,1.00000]

提示：

1. count.length == 256
2. 1 <= sum(count) <= 10^9
3. 计数表示的众数是唯一的
4. 答案与真实值误差在 10^-5 以内就会被视为正确答案

---

20ms

class Solution {
    func sampleStats(_ count: [Int]) -> [Double] {
        guard count.count == 256 else { 
            assert(1 == 0, "Input error") 
        }
        var result = [Double]()
        var left = 0
        var right = 255
        while left <= 255 && count[left] == 0 {
            left += 1
        }
        
        while right > left && count[right] == 0 {
            right -= 1
        }
        
        result.append(Double(left))
        result.append(Double(right))
        
        var counter = 0
        var sum = 0
        var mode = 0
        var modeCounter = 0
        for i in count.indices {
            if count[i] > modeCounter {
                modeCounter = count[i]
                mode = i
            }
            counter += count[i]
            sum += i * count[i]
        }
        result.append(Double(sum) / Double(counter))
        
        var start = counter % 2 != 0 ? counter / 2 + 1 : counter / 2
        for i in 0..<count.count {
            if start - count[i] > 0 {
                // print(start)
                // print(i)
                start -= count[i]
                continue
            }
            
            if counter % 2 != 0 {
                result.append(Double(i))
                break
            } else {
                if start - count[i] == 0 {
                    var curr = i + 1
                    
                    while curr <= 255 && count[curr] == 0 {
                        curr += 1
                    } 
                    result.append(Double(curr + i) / Double(2))
                    break
                } else if start - count[i] < 0 {
                    result.append(Double(i))
                    break
                } 
            }
        }

        result.append(Double(mode))
        return result
    }
}

---

Runtime: 24 ms

Memory Usage: 21.2 MB

class Solution {
    func sampleStats(_ count: [Int]) -> [Double] {
        var L:Int = 0
        var R:Int = 255
        while(L < 256 && count[L] == 0)
        {
            L += 1
        }
        while(L >= 0 && count[R] == 0)
        {
            R -= 1
        }
        let n:Int = count.reduce(0,+)
        var sum:Double = 0
        for i in 0...255
        {
            sum += Double(i * count[i])
        }
        let ave:Double = sum / Double(n)
        var cur:Int = 0
        var mid:Double = 0
        if (n & 1) != 0
        {
            cur = 0
            for i in 0...255
            {
                cur += count[i]
                if cur >= (n + 1) / 2
                {
                    mid = Double(i)
                    break
                }
            }
        }
        else
        {
            let x:Int = n / 2
            let y:Int = x + 1
            cur = 0
            for i in 0...255
            {
                cur += count[i]
                if cur >= x
                {
                    mid += Double(i)
                    break
                }
            }
            cur = 0
            for i in 0...255
            {
                cur += count[i]
                if cur >= y
                {
                    mid += Double(i)
                    break
                }
            }
            mid /= 2
        }
        let max_freq:Int = count.max() ?? Int.max
        var mode:Double = -1.0
        for i in 0...255
        {
            if count[i] == max_freq
            {
                mode = Double(i)
            }
        }
        return [Double(L), Double(R), ave, mid, mode]
    }
}

---

36ms

 

class Solution {
  func sampleStats(_ count: [Int]) -> [Double] {
    var minN = Int.max
    var maxN = Int.min
    var median: Double = 0
    var mode = 0
    var modeVal = 0
    var countOfNum = 0
    var sumVal = 0
    for pair in count.enumerated() {
      if pair.element != 0 {
        minN = min(minN, pair.offset)
        maxN = max(maxN, pair.offset)
        if pair.element > mode {
          mode = pair.element
          modeVal = pair.offset
        }
        sumVal += pair.offset * pair.element
        countOfNum += pair.element
      }
    }
    
    if countOfNum % 2 == 1 {
      median = Double(valueBy(index: countOfNum/2, a: count))
    } else {
      median = Double(valueBy(index: countOfNum/2, a: count) + valueBy(index: countOfNum/2 - 1, a: count))/2
    }
    
    return [Double(minN), Double(maxN), Double(sumVal)/Double(countOfNum), median, Double(modeVal)]
  }
  
  func valueBy(index: Int, a: [Int]) -> Int {
    var curentIndex = 0
    for pair in a.enumerated() {
      curentIndex += pair.element
      if curentIndex > index {
        return pair.offset
      }
    }
    fatalError()
  }
}