前缀和算法题2

/**
     * https://leetcode.cn/problems/subarray-sums-divisible-by-k/description/
     * 1.同余定理：如果(a-b)/p=k  k为整数，则a%p=b%p
     * 2.C++和Java中对[负数%正数]的结果以及修正：
     * 负%正=负    修正：(a%p+p)%p
     * */
    public static void hanShu6(int[] nums, int target){
        Map<Integer,Integer> hash=new HashMap<Integer,Integer>();
        hash.put(0%target,1);
        int sum=0,ret=0;
        for (int x :
                nums) {
            sum += x;
            int r=(sum%target+target)%target;
            ret+=hash.getOrDefault(r,0);
            hash.put(r,hash.getOrDefault(r,0)+1);
        }
    }

 

/**
     * https://leetcode.cn/problems/subarray-sum-equals-k/
     * 见图
     * */
    public static void hanShu5(int[] nums, int target){
        Map<Integer,Integer> hash=new HashMap<Integer,Integer>();
        hash.put(0,1);
        int sum=0,ret=0;
        for (int x :
                nums) {
            sum += x;
            ret+=hash.getOrDefault(sum-target,0);
            hash.put(sum,hash.getOrDefault(sum,0)+1);
        }
    }