leetcode 1011

星环一面最后让写的题，一开始我在想怎么把原始数组拆分成多段然后分段求和，面试官提醒了我一下答案有个最小值和最大值，我马上反应过来是个二分查找，然后很快写完了。

注意判断当前值是否合法的valid方法里初始天数为1，我一开始写的0，面试官提醒我在结尾用 expectedDay + 1 <= days 判断，但是后来想了下，初始天数为1比较合理。

class Solution {
    public int shipWithinDays(int[] weights, int days) {
        int sum = 0;
        int min = weights[0];
        for(int w : weights){
            sum += w;
            min = Math.max(min, w);
        }
        int max = sum;
        while(min < max){
            int mid = min + ((max - min) >> 1);
            //System.out.println(mid+" "+valid(mid, weights, days));
            if(valid(mid, weights, days)){
                max = mid;
            }else{
                min = mid + 1;
            }
        }
        return min;
    }
    private boolean valid(int mid, int[] weights, int days){
        int expectedDay = 1;
        int tempSum = 0;
        for(int w : weights){
            if(tempSum + w <= mid){
                tempSum += w;
            }else{
                tempSum = w;
                expectedDay++;
            }
        }
        //System.out.println(mid + " " + expectedDay);
        return expectedDay <= days;
    }
}