1248. Count Number of Nice Subarrays

Link

Solution

將問題簡化成求subarrays sum值 = k的問題 560:

nums[i] = nums[i] % 2

 public int numberOfSubarrays(int[] nums, int k) {
        int ret = 0;
        for(int i = 0; i < nums.length; i++){
            nums[i] = nums[i]%2;
        }
        
        HashMap<Integer, Integer> map = new HashMap<>();
        
        int count = 0;
        for(int i = 0 ; i < nums.length; i++){
            count += nums[i];
            
            if(count == k){
                ret++;
            }
            
            ret += map.getOrDefault((count-k),0);
            
            map.compute(count, (ks, v)->{
               if(v == null) return 1;
                else return v+1;
            });
        }
        return ret;
        
    }