def partition(data,start,last):
if data is None:
return None
if start < 0 or last < 0:
return None
if last <= start:
return start
mid_num = data[start]
while start < last:
while start < last and mid_num <= data[last]:
last -= 1
data[start] = data[last]
while start < last and data[start] <= mid_num:
start += 1
data[last] = data[start]
data[start] = mid_num
return start
def find_kth_num(data,k):
if data is None:
return None
if k >= len(data):
return None
start = 0
last = len(data) - 1
index = partition(data,start,last)
while index != k:
if k < index:
last = index - 1
index = partition(data,start,last)
else:
start = index + 1
index = partition(data,start,last)
return data[k]
def more_than_half_num(data):
elem = find_kth_num(data,len(data)//2)
cnt = 0
for _ in data:
if _ == elem:
cnt += 1
if cnt > len(data)//2:
return elem
else:
return None
def main():
data = [5,4,2,2,2]
num = more_than_half_num(data)
print(num)
解法2：
def more_than_half_num2(data):
num = None
times = 0
for item in data:
if times == 0:
num = item
times = 1
elif num == item:
times += 1
elif num != item:
times -= 1
if times > 0:
return num
else:
return None
