LeetCode 123 Best Time to Buy and Sell Stock III (C++, Python)

-
Follow up for N-Queens problem.
Now, instead outputting board configurations, return the total number of distinct solutions.

Say you have an array for which the ith element is the price of a given stock on day i.
Design an algorithm to find the maximum profit. You may complete at most two transactions.
Note:
You may not engage in multiple transactions at the same time (ie, you must sell the stock before you buy again)
Solution (C++) 


 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
class Solution {
public:
    int maxProfit(vector<int>& prices) {
        int profit = 0;
        if (prices.empty()) return 0;
        const int N = prices.size();
        vector<int> maxprices(N, 0);
        int tmpmaxprice = numeric_limits<int>::min();
        for (int i = N - 1; i >= 0; --i) {
            tmpmaxprice = max(tmpmaxprice, prices[i]);
            maxprices[i] = tmpmaxprice;
        }
        vector<int> firstprofits(N, 0);
        int tmpminprice = numeric_limits<int>::max();
        int tmpmaxprofit = 0;
        for (int i = 0; i < N; ++i) {
            tmpminprice = min(tmpminprice, prices[i]);
            tmpmaxprofit = max(tmpmaxprofit, prices[i] - tmpminprice);
            firstprofits[i] = tmpmaxprofit;
        }
        for (int i = 2; i <= N; ++i) {
            // second transaction buy on day i
            int secondprofit = (i == N)? 0: (maxprices[i] - prices[i]);
            profit = max(profit, firstprofits[i - 1] + secondprofit);
        }
        return profit;
    }
};
Solution (Python)


 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
class Solution:
    # @param {integer[]} prices
    # @return {integer}
    def maxProfit(self, prices):
        N = len(prices)
        if N <= 1: return 0
        minPrices = [None] * N 
        tmpMinPrice = None
        for i in range(N):
            if tmpMinPrice is None:
                tmpMinPrice = prices[i]
            else:
                tmpMinPrice = min(tmpMinPrice, prices[i])
            minPrices[i] = tmpMinPrice
        secondProfits = [None] * N
        tmpMaxPrice = None
        tmpMaxProfit = None
        for i in range(N - 1, -1, -1):
            if tmpMaxPrice is None:
                tmpMaxPrice = prices[i]
            else:
                tmpMaxPrice = max(tmpMaxPrice, prices[i])
            if tmpMaxProfit is None:
                tmpMaxProfit = tmpMaxPrice - prices[i]
            else:
                tmpMaxProfit = max(tmpMaxProfit, tmpMaxPrice - prices[i])
            secondProfits[i] = tmpMaxProfit
        ret = 0
        # first transaction sold on day i
        for i in range(N):
            firstProfit = prices[i] - minPrices[i]
            secondProfit = secondProfits[i]
            ret = max(ret, firstProfit + secondProfit)
        return ret

Popular posts from this blog

How Django Works (4) URL Resolution

-
Image
Why We Need URL Resolution Theoretically, we could write a single function to process all incoming HTTP requests. It would work well for very simple websites. For any real websites, it would be much more appropriate to categorize HTTP requests based on their URLs and process them separately in different handlers. For example, BASEURL/polls/ would be an application for polls whereas BASEURL/blogs/ would be an application for blogs. This way, different URLs can be considered different logic applications, so we can think of websites in terms of logic applications – a higher level of abstraction that HTTP request/response pairs. Fortunately, many modern web frameworks come default with mechanisms that do the categorization of HTTP requests based on URIs, which spares us the effort of having to reinvent the wheel.   Django's URL Resolution The official Django document has following description about how Django processes a request. https://docs.djangoproject.com/en/1.8/topic...
Read more

Python Class Method and Class Only Method

-
In this post, I will be discussing Python method especially class method. Example class Foo : def bar_inst ( self ): print ( self , "This is bar_inst" ) @staticmethod def bar_static (): print ( "This is bar_static" ) @classmethod def bar_class (cls): print (cls, "This is bar_class" ) >>> foo = Foo() >>> foo.bar_inst <bound method Foo.bar_inst of <test.Foo object at 0x025A0EB0>> >>> foo.bar_static <function Foo.bar_static at 0x025A34F8> >>> foo.bar_class <bound method type.bar_class of <class 'test.Foo'>> foo.bar_static just returns a function object as if bar_static were defined outside of class. (In Python 2, it would return an unbound method; Python 3 has removed the concept of unbound methods. So a function is either a bound method or a regular function object) How It Works -- Descriptor  Every ...
Read more

How Django works (3): Testing Server and Static Files Serving

-
How Django Handles Static Files By default, Django installs an Application django.contrib.staticfiles, which is responsible for handling requests to files under STATIC_URL.   INSTALLED_APPS = ( 'django.contrib.admin' , 'django.contrib.auth' , 'django.contrib.contenttypes' , 'django.contrib.sessions' , 'django.contrib.messages' , 'django.contrib.staticfiles' , 'polls' , ) STATIC_URL = '/static/' This method is grossly inefficient and probably insecure, so it is unsuitable for production. https://docs.djangoproject.com/en/1.8/howto/static-files/deployment/ How staticfiles App Works Based on the first blog of Django series, Django interacts with web servers by providing a callable application that conforms to WSGI specification. 1 2 3 4 5 class WSGIHandler (base . BaseHandler): initLock = Lock() request_class = WSGIRequest def __call__ ( self , environ, start_...
Read more