[Swift]LeetCode875. 爱吃香蕉的珂珂 | Koko Eating Bananas

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➤微信公众号：山青咏芝（shanqingyongzhi）
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Koko loves to eat bananas.  There are N piles of bananas, the i-th pile has piles[i]bananas.  The guards have gone and will come back in H hours.

Koko can decide her bananas-per-hour eating speed of K.  Each hour, she chooses some pile of bananas, and eats K bananas from that pile.  If the pile has less than Kbananas, she eats all of them instead, and won't eat any more bananas during this hour.

Koko likes to eat slowly, but still wants to finish eating all the bananas before the guards come back.

Return the minimum integer K such that she can eat all the bananas within H hours. 

Example 1:

Input: piles = [3,6,7,11], H = 8
Output: 4

Example 2:

Input: piles = [30,11,23,4,20], H = 5
Output: 30

Example 3:

Input: piles = [30,11,23,4,20], H = 6
Output: 23 

Note:

• 1 <= piles.length <= 10^4
• piles.length <= H <= 10^9
• 1 <= piles[i] <= 10^9

---

珂珂喜欢吃香蕉。这里有 N 堆香蕉，第 i 堆中有 piles[i] 根香蕉。警卫已经离开了，将在 H 小时后回来。

珂珂可以决定她吃香蕉的速度 K （单位：根/小时）。每个小时，她将会选择一堆香蕉，从中吃掉 K 根。如果这堆香蕉少于 K 根，她将吃掉这堆的所有香蕉，然后这一小时内不会再吃更多的香蕉。  

珂珂喜欢慢慢吃，但仍然想在警卫回来前吃掉所有的香蕉。

返回她可以在 H 小时内吃掉所有香蕉的最小速度 K（K 为整数）。 

示例 1：

输入: piles = [3,6,7,11], H = 8
输出: 4

示例 2：

输入: piles = [30,11,23,4,20], H = 5
输出: 30

示例 3：

输入: piles = [30,11,23,4,20], H = 6
输出: 23 

提示：

• 1 <= piles.length <= 10^4
• piles.length <= H <= 10^9
• 1 <= piles[i] <= 10^9

---

340ms

class Solution {
    func minEatingSpeed(_ piles: [Int], _ H: Int) -> Int {
        var minSpeed = 1, maxSpeed = 1000_00
        while minSpeed < maxSpeed {
            let speed = (maxSpeed + minSpeed) / 2
            if possible(piles, speed, H) { maxSpeed = speed }
            else { minSpeed = speed + 1}
        }
        return minSpeed
    }

    func possible(_ piles: [Int], _ speed: Int, _ H: Int) -> Bool {
        var time = 0
        for p in piles { time += (p-1)/speed + 1 }
        return H >= time
    }
}

---

Runtime: 420 ms

Memory Usage: 19.1 MB

class Solution {
    func minEatingSpeed(_ piles: [Int], _ H: Int) -> Int {
        var l:Int = 1
        var r:Int = 1000_000_000
        while (l < r)
        {
            var m:Int = (l + r) / 2
            var total:Int = 0
            for p in piles
            {
                total += (p + m - 1) / m
            }
            if total > H
            {
                l = m + 1
            }
            else
            {
                r = m
            }
        }
        return l
    }
}

---

444ms

class Solution {
    func minEatingSpeed(_ piles: [Int], _ H: Int) -> Int {
        guard piles.count > 0 else {
            return 0
        }
        var r = piles.max()! + 1
        if piles.count == H {
            return r - 1
        }
        var l = 1
        while l < r {
            let m = l + (r - l) / 2
            ///get how many hours using m
            var hours = 0
            for p in piles {
                hours += (p + m - 1) / m
            }
            if hours <= H {
                r = m
            } else {
                l = m + 1
            }
        }
        return l
    }
}

---

456ms

class Solution {
    func isGood(_ piles: [Int], _ H: Int, _ K: Int) -> Bool {
        var total = 0
        for item in piles {
            if item % K == 0 {
                total =  total + item / K
            } else {
                total =  total + item / K + 1
            }
            if total > H {
                return false
            }
        }
        return true
    }
    
    func minEatingSpeed(_ piles: [Int], _ H: Int) -> Int {
        if piles.count == 0 || H <= 0{
            return 0
        }
        
        var end = piles[0]
        for item in piles {
            end = max(end, item)
        }
        
        var begin = 1
        while(begin<=end){
            let middle = (begin+end)/2
            if isGood(piles, H, middle) {
                end = middle - 1
            } else {
                begin = middle + 1
            }
        }
        return begin
    }
}