ARTS Week 25

Algorithm

This week's LeetCode titled 371. Sum of two integers

Here are two integers a and b, Don't use Operator + and -, Calculates and returns the sum of two integers .

 Input ：a = 1, b = 2
 Output ：3

According to the four cases of adding two binary bits, they are as follows ：

0 + 0 = 0
0 + 1 = 1
1 + 0 = 1
1 + 1 = 0 ( carry )

Without considering carry , nothing The result of carry addition is a^b; Whether to carry or not depends on a&b, Therefore, the result of carry is (a&b)<<1. therefore , We can put integers a and b And , Split into a and b The sum of the non carry addition result and the carry result . Because each split can shift the lowest bit to the left by at least one bit , Again because a and b You can take a negative number . Because signed integers are represented by complements , therefore 0 And negative numbers also apply to the above methods .

class Solution {
    public int getSum(int a, int b) {
        while (b != 0) {
            int carry = (a & b) << 1;
            a = a ^ b;
            b = carry;
        }
        return a;
    }
}

Review

This week, Review The English article is ： Best practices for writing code comments

Too many code comments do not guarantee their quality , Good comments should help others understand the code more easily , Here are some suggestions on how to ensure code quality ：

1. Comments should not duplicate code .

Bad examples

i = i + 1;         // Add one to i

A more extreme example of error

// create a for loop // <-- comment
for // start for loop
(   // round bracket
    // newline
int // type for declaration
i    // name for declaration
=   // assignment operator for declaration
0   // start value for i

2. Good comments cannot be an excuse for unclear code .

Bad examples , Variable n The meaning of is not clear

private static Node getBestChildNode(Node node) {
    Node n; // best child node candidate
    for (Node node: node.getChildren()) {
        // update n if the current state is better
        if (n == null || utility(node) > utility(n)) {
            n = node;
        }
    }
    return n;
}

A good example , The variable should be n Renamed as bestNode, This is enough for others to understand without comments .

private static Node getBestChildNode(Node node) {
    Node bestNode;
    for (Node currentNode: node.getChildren()) {
        if (bestNode == null || utility(currentNode) > utility(bestNode)) {
            bestNode = currentNode;
        }
    }
    return bestNode;
}

3. If you can't write clear notes , There may be a problem with the code .Unix The most notorious comment in the source code is “You are not expected to understand this（ You shouldn't understand this ）”, Unfortunately , Dennis Ritchie who wrote these notes , He doesn't fully understand the code himself , Later I had to rewrite the code .

4. Comments should eliminate confusion , Instead of causing confusion . If your code comments cause ambiguity , Please delete it .

5. Explain the single code in the comments .

Bad examples , Code should not explain code that everyone can understand , Unless you're writing tutorials for novices .

final Object value = (new JSONTokener(jsonString)).nextValue();
// Note that JSONTokener.nextValue() may return
// a value equals() to null.
if (value == null || value.equals(null)) {
    return null;
}

6. Provide a link to the original source of the copied code . Here is a good example ：

/** Converts a Drawable to Bitmap. via https://stackoverflow.com/a/46018816/2219998. */
return (int) (0.3 * red + 0.59 * green + 0.11 * blue);

7. Include links to external references where they are most helpful . occasionally , You can also give a link to the manual ：

// http://tools.ietf.org/html/rfc4180 suggests that CSV lines
// should be terminated by CRLF, hence the \r\n.
csvStringBuilder.append("\r\n");

8. Add comments when fixing errors . Here is a good example ：

// NOTE: At least in Firefox 2, if the user drags outside of the browser window,
// mouse-move (and even mouse-down) events will not be received until
// the user drags back inside the window. A workaround for this issue
// exists in the implementation for onMouseLeave().
@Override
public void onMouseMove(Widget sender, int x, int y) { .. }

9. Use annotations to mark incomplete implementations . Here's an example ：

// TODO(hal): We are making the decimal separator be a period, 
// regardless of the locale of the phone. We need to think about 
// how to allow comma as decimal separator, which will require 
// updating number parsing and other places that transform numbers 
// to strings, such as FormatAsDecimal

in fact , Many code comments are actually the same as shown in the figure below ：

Tip

clock() Functions and gettimeofday() Similarities and differences of functions ：

• Common ground ： Both can get the current time , By calculating the difference between the current time before and after , Then get the running time of a piece of code
• Difference ：clock() yes C Library functions , This means that it can be used in any system ; and gettimeofday() Functions are just Linux Functions in the system , Therefore, it can only be used in Linux The system uses .

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Released C Language reading and writing CSV The tutorial trilogy , The reading data of each platform is significantly better than ARTS Many series , It can be seen that the platform and everyone prefer tutorials with specific points , More articles of this type will be created in the future .