后缀和

N, L = map(int, input().split())
arr = list(map(int, input().split()))

n = 100010

d = [0] * n
dd = [0] * n

for i in range(N):
    d[arr[i]] += 1

dd[-1] = d[-1]
for i in range(n-1, 0, -1):
    dd[i - 1] = dd[i] + d[i - 1]

ans = 0
for i in range(N+1, 0, -1):
    if dd[i] + min(d[i - 1], L) >= i:
        ans = i
        break
print(ans)

二分

N, L = map(int, input().split())
arr = list(map(int, input().split()))

def acq(h, L):
    count = 0
    reL = L
    for i in range(N):
        if arr[i] >= h:
            count += 1
        elif count < h and reL > 0 and arr[i] >= h - 1:
            reL -= 1
            count += 1
    return count >= h

left, right = 0, N
while left < right:
    mid = (left + right + 1) // 2
    if acq(mid, L):
        left = mid
    else:
        right = mid - 1

print(left)

双指针

N, L = map(int, input().split())
arr = list(map(int, input().split()))
arr.sort(reverse=True)

ans = 0
for i in range(0, N):
    j = i - L + 1
    while j > 0 and arr[j - 1] < i + 1:
        j -= 1
    if arr[i] >= i and i - j + 1 <= L:
        ans = i+1

print(ans)

贪心

N, L = map(int, input().split())
arr = list(map(int, input().split()))
arr.sort()
ans = []

l, r = 0, 0
while r < N:
    if arr[l] == arr[r]:
        r += 1
    elif arr[l] + 1 < arr[r]:
        ans.append(min(N - l, N - r + L, N - l - 1))
        l += 1
    else:
        ans.append(min(N - l, N - r + L, 1 + arr[l]))
        l += 1

    if r >= N:
        break

if not ans:
    if L >= N:
        print(arr[0] + 1)
    else:
        print(max(arr[0], L))
else:
    print(max(ans))