题解 | #放苹果#

m,n = list(map(int,input().split()))
nums = list(range(m+1))
res = 0
def backtrack(start, path, target):
    global res
    if len(path)==n and target==0:
        #res.append(path[:])
        res +=1
        return 
    elif len(path)==n:
        return 
    for i in range(start,m+1):
        num = nums[i]
        if num > target:
            break
        path.append(num)
        backtrack(i,path,target-num)
        path.pop()
backtrack(0, [], m)
print(res)