lintcode-子数组的最大平均值 II

一.题目描述

给出一个整数数组，有正有负。找到这样一个子数组，他的长度大于等于 k，且平均值最大。

二.代码

public double maxAverage(int[] nums, int k) {
        double left = Double.MAX_VALUE;
        double right = Double.MIN_VALUE;
        for (int num : nums) {
            left = Math.min(num, left);
            right = Math.max(num, right);
        }
        while (left + 0.00001 < right) {
            double mid = (left + right) / 2;
            if (check(nums, k, mid)) {
                left = mid;
            } else {
                right = mid;
            }
        }
        return left;
    }

    private boolean check(int[] nums, int k, double avg) {
        double rightSum = 0, leftSum = 0, minLeftSum = 0;
        for (int i = 0; i < k; i++) {
            rightSum += nums[i] - avg;
        }
        if (rightSum >= 0) {
            return true;
        }
        for (int i = k; i < nums.length; i++) {
            rightSum += nums[i] - avg;
            leftSum += nums[i - k] - avg;
            minLeftSum = Math.min(minLeftSum, leftSum);
            if (rightSum >= minLeftSum) {
                return true;
            }
        }
        return false;
    }