Bit operation of code

 java Middle displacement operation “＜＜“,“＞＞“,“＞＞＞“

 （1）"<<" For left shift operation

Whether positive or negative , Low complement 0;

（2） “>>” Shift right

If it's a positive number , Then the high position will be supplemented 0;

If it's negative , Then the high position will be supplemented 1;

（3） “>>>” For unsigned right shift operation

Whether positive or negative , All high places are filled 0;

Binary 1 The number of

public class Solution {
    public int NumberOf1(int n) {
        int res=0;
        for(int i=0;i<32;++i){   // Attention bit operation  & |
            if((n & 1<<i)!=0)    // Notice here is  1<<i, Move left i position 
                ++res;
        }
        return res;
    }
}

// characteristic n&(n−1), Will n The lowest bit in the binary of is determined by 1 become 0
public class Solution {
    public int NumberOf1(int n) {
        int res=0;
        while (n!=0){
            n&=(n-1);
            ++res;
        }
        return res;
    }
}

Power operation

// Direct calculation 
public class Solution {
    public double Power(double base, int exponent) {
        if(exponent<0){
            base=1/base;
            exponent=-exponent;
        }
        double res=1.0;
        for(int i=0;i<exponent;++i)
            res*=base;
        return res;   
  }
}

public class Solution {
    public double Power(double base, int exponent) {
        if(exponent<0){
            base=1/base;
            exponent=-exponent;
        }
        return mypower(base,exponent);
    }

    public double mypower(double x,int y){
        double res = 1;
        while(y != 0){         // This is similar to divide and conquer 
            if((y & 1) != 0)
                res *= x;
            x *= x;
            y = y >> 1;
        }
        return res;
    }
}

String to number （ Digital output in [2^-32,2^32-1] Between ）

import java.util.*;
public class Solution {
    public static int StrToInt (String s) {
        if(s==null && s.length()==0) return 0;
        String string=s.trim();
        if(string.length()==0) return 0;
        boolean flag=true;
        char numone=string.charAt(0);
        long res=0;                    // Notice that this is Long Ah ah ah 
        if(!num(numone) && numone!='-' && numone!='+') return 0;
        if(numone=='-') flag=false;
        else if(numone=='+') flag=true;
        else res=numone-'0';
        for(int i=1;i<string.length();++i){
            char c=string.charAt(i);
            if(!num(c))
                break;
            else{
                res=res*10+(c-'0');   // Otherwise, it will calculate according to overflow , The latter judgment doesn't work at all 
                if(flag && res>Integer.MAX_VALUE) return Integer.MAX_VALUE;
                if(!flag && res*(-1)<Integer.MIN_VALUE) return Integer.MIN_VALUE;
            }
        }
        if(flag) return (int) res;
        else return  (int) -res;
    }

    public static boolean num(char c){
        if(c>='0' && c<='9')
            return true;
        else return false;
    }
}