lcp336

统计范围内的元音字符串数

方法一：HashSet

class Solution {
    public int vowelStrings(String[] words, int left, int right) {
        int res = 0;
        Set<Character> set = new HashSet<>();
        set.add('a');
        set.add('e');
        set.add('i');
        set.add('o');
        set.add('u');
        for (int i = left; i <= right; ++i) {
            String str = words[i];
            if (set.contains(str.charAt(0)) && set.contains(str.charAt(str.length() - 1)))
                ++res;
        }
        return res;
    }
}

重排数组以得到最大前缀分数

方法一：贪心

class Solution {
    public int maxScore(int[] nums) {
        int n = nums.length, res = 0;
        Arrays.sort(nums);
        long[] preSum = new long[n + 1];
        for (int i = n - 1; i >= 0; --i) {
            preSum[i] = preSum[i + 1] + nums[i];
            if (preSum[i] > 0)
                ++res;
            else 
                break;
        }
        return res;
    }
}

统计美丽子数组数目

方法一：求异或和等于0 的子数组个数

class Solution {
    public long beautifulSubarrays(int[] nums) {
        int n = nums.length;
        long res = 0;
        int[] s = new int[n + 1];
        for (int i = 0; i < n; ++i)
            s[i + 1] = s[i] ^ nums[i];
        Map<Integer, Integer> cnt = new HashMap<>();
        for (int x : s) {
            res += cnt.getOrDefault(x, 0);
            cnt.put(x, cnt.getOrDefault(x, 0) + 1);
        }
        return res;
    }
}

完成所有任务的最少时间

方法一：