剑指 Offer II 073. 狒狒吃香蕉（875. 爱吃香蕉的珂珂 ）

题目：

 

 

 

思路：

【1】本质上的思路是采用二分查找

代码展示：

标准的二分查找的方式：

//时间6 ms击败99.29%
//内存42.5 MB击败28.75%
class Solution {
    public int minEatingSpeed(int[] piles, int h) {
        int low = 1;
        int high = 0;
        for (int pile : piles) {
            high = Math.max(high, pile);
        }
        int k = high;
        while (low < high) {
            int speed = (high - low) / 2 + low;
            long time = getTime(piles, speed);
            if (time <= h) {
                k = speed;
                high = speed;
            } else {
                low = speed + 1;
            }
        }
        return k;
    }

    public long getTime(int[] piles, int speed) {
        long time = 0;
        for (int pile : piles) {
            //这里是为了向上取整，因为（speed - 1） / speed = 0；但如果多加上一个1就会变为1
            int curTime = (pile + speed - 1) / speed;
            time += curTime;
        }
        return time;
    }
}

优化的写法：

//时间0 ms击败100%
//内存42.2 MB击败79.9%
class Solution {
    public int minEatingSpeed(int[] piles, int h) {
        int n = piles.length;
        long sum = 0;
        for (int num : piles) {
            sum += num;
        }
        int left = (int)(sum / h + (sum % h == 0 ? 0 : 1));
        int right = (int)(sum / (h - n + 1)) + 1;
        while(left<right){
            int mid =left+(right-left>>1);
            int time =0;
            for(int p : piles){
                time += (p + mid - 1) / mid;
            }
            if(time<=h)right=mid;
            else left=mid+1;
            
        }
        return left;
    }
}