算法题题解记录——5. 寻找最大葫芦

题目

www.marscode.cn/practice/r3…

思路

用dict存{ 数值: 出现的次数 }，定义一个自定义的降序顺序数组 [1, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2]，两层遍历找符合条件的a，b。第一次符合的即为最大的葫芦。

代码

def solution(n, max, array):
    # Edit your code here
    arr = [1, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2]
    num_count = {}
    for num in array:
        if num_count.get(num) is None:
            num_count[num] = 1
        else:
            num_count[num] += 1
    for a in arr:
        a_count = num_count.get(a)
        if (a_count is not None and a_count >= 3):
            for b in arr:
                if a == b:
                    continue
                b_count = num_count.get(b)
                if (b_count is not None and b_count >= 2):
                    total = a * 3 + b * 2
                    if (total <= max):
                        return [a, b]
    return [0, 0]


if __name__ == "__main__":
    # Add your test cases here

    print(solution(9, 34, [6, 6, 6, 8, 8, 8, 5, 5, 1]) == [8, 5])
    print(solution(9, 37, [9, 9, 9, 9, 6, 6, 6, 6, 13]) == [6, 9])
    print(solution(9, 40, [1, 11, 13, 12, 7, 8, 11, 5, 6]) == [0, 0])

复杂度

• 时间复杂度

  dict记录 O(N)，两层for循环 O(n²)，取最大系数即O(n²)

• 空间复杂度 O(n)

学到了

1. python中遍历dict键的方法：

my_dict = {'a': 1, 'b': 2, 'c': 3}
for key in my_dict: 
    print(key)

for key in my_dict.keys():
    print(key)
    
for key, value in my_dict.items(): 
    print(key)

2. python中没有 ===（严格相等运算符），比较地址使用 is：

a = [1, 2]
b = [1, 2]
print(a == b) # 比较的是值 True
print(a is b) # 比较的是地址 False