Practice Java functions and algorithms every day Math functions summary and string conversion integers

Notice：

The blank characters in this question include only space characters ' ' 。
Except for the leading space or number, the rest of the string，Do not ignore it Any other character。
 

Example 1：
 
enter：s = "42"
Output：42
explain：The bold string is a character that has been read.，The caret is the currently read character。
The 1 step："42"（No characters are read in at present，Because there are no leading spaces）
         ^
The 2 step："42"（No characters are read in at present，Because it doesn't exist here '-' or '+'）
         ^
The 3 step："42"（Read in "42"）
           ^
Analyze the integer 42 。
because "42" In range [-231, 231 - 1] Inside，The final result is 42 。

Example 2：
 
enter：s = "   -42"
Output：-42
explain：
The 1 step："   -42"（Read into leading spaces，But ignore it）
            ^
The 2 step："   -42"（Read in '-' character，So the result should be a negative number）
             ^
The 3 step："   -42"（Read in "42"）
               ^
Analyze the integer -42 。
because "-42" In range [-231, 231 - 1] Inside，The final result is -42 。

Example 3：
 
enter：s = "4193 with words"
Output：4193
explain：
The 1 step："4193 with words"（No characters are read in at present，Because there are no leading spaces）
         ^
The 2 step："4193 with words"（No characters are read in at present，Because it doesn't exist here '-' or '+'）
         ^
The 3 step："4193 with words"（Read in "4193"；Since the next character is not a number，所以Read in停止）
             ^
Analyze the integer 4193 。
because "4193" In range [-231, 231 - 1] Inside，The final result is 4193 。

Example 4：
 
enter：s = "words and 987"
Output：0
explain：
The 1 step："words and 987"（No characters are read in at present，Because there are no leading spaces）
         ^
The 2 step："words and 987"（No characters are read in at present，Because it doesn't exist here '-' or '+'）
         ^
The 3 step："words and 987"（Due to the current character 'w' Not a number，So read in and stop）

Example 5：

enter：s = "-91283472332"
Output：-2147483648
explain：
The 1 step："-91283472332"（No characters are read in at present，Because there are no leading spaces）
         ^
The 2 step："-91283472332"（Read in '-' character，So the result should be a negative number）
          ^
The 3 step："-91283472332"（Read in "91283472332"）
                     ^
Analyze the integer -91283472332 。
because -91283472332 Less than range [-231, 231 - 1] The lower boundary of，The final result is truncated as -231 = -2147483648 。
 

 Recorded pi
 RecordeConstant
Math中还有一些类似Constant，All are common engineering mathematics。
 Find the absolute value
 Sine function  反Sine function
 Cosine function  反Cosine function
 Tangent function  反Tangent function Math.atan2 商的反Tangent function
 Convert radians into angles  Angle converted to radians
[color=red] Get the maximum integer not less than a certain number A larger number than it[/color]
[color=red] Get the maximum integer no greater than a certain number A smaller number than it[/color]
 Ask for rest
 Find the largest of the two numbers
 Find the smallest of two numbers
 Please give me a prescription
[color=red] Find any power of a certain number, Throw outArithmeticExceptionHandle overflow exceptions[/color]
 begeAny power of
Math.log10 by10Logarithm at base
 Natural logarithm
 beg距离某数最近的整数（Probably larger than some，Maybe smaller than it）
[color=red] beg距离某数最近的整数，returnintType orlongtype（上一个函数returndoubletype）[/color]
 return0，1A random number between

public class test {
	public static String myAtoi(String s) {
		char[] list=();
		StringBuilder lis=new StringBuilder();
		for(int i=0;i<;i++) {
			if(list[i]==' ') {
				continue;
			}
			else if(list[i]=='+'||list[i]=='-'||((list[i])>=48&&(list[i])<=57)) {
				(list[i]);
			}else {
				return ();
			}
		}
		return ();
	}
	public static void main(String[] args) {
		long a=(myAtoi("words and 987")==""? "0":myAtoi("words and 987"));
		int b= (int) ((a, (2, 31)-1), (-2, 31));
		(b);
		
	}

}

public static String myAtoi(String s) {
		//The following two lines are what I mentioned earlier to turn a string into a character array		char[] list=();
		StringBuilder lis=new StringBuilder();
		//The following mainly uses character length as the number of times to convert characters into integers		for(int i=0;i<;i++) {
		//According to the question requirements, start to encounter spaces and discard useless leading spaces			if(list[i]==' ') {
			//I won't introduce the function of continue, it's basic.				continue;
			}//The following judgment is introduced in detail below			else if(list[i]=='+'||list[i]=='-'||((list[i])>=48&&(list[i])<=57)) {
				(list[i]);
			}else {//If you encounter characters other than the above conditions, you will end directly and return to the string				return ();
			}
		}
		return ();
	}

else if(list[i]=='+'||list[i]=='-'||((list[i])>=48&&(list[i])<=57)) {
				(list[i]);

else if(list[i]=='+'||list[i]=='-'||(list[i]>='0'&&list[i]<='9')) {
				(list[i]);

public static void main(String[] args) {
//The three-point operation is involved, but we have talked about the rules before. The main function here is to prevent the following situation from returning to a null character, so we will turn it to zero  long a=(myAtoi("words and 987")==""? "0":myAtoi("words and 987"));
  //This is the main usage of the Math function mentioned above, because the answer must be judged by the scope  //So let us first find the number sum of the upper bound (2^31)-1 to find the smallest  //Compare with -2^31 to find the largest number. We are looking for. If you don’t understand, you can send a private message or comment for detailed explanation.  int b= (int) ((a, (2, 31)-1), (-2, 31));
  (b);