Sword finger offer | number of 1 in binary

Enter an integer n , Output the number 32 In bit binary representation 1 The number of . Negative numbers are represented by complements .

Method 1：

Method 1： take 32 Every one is associated with 1 Meet each other . Statistics 1 The number of .

 public int NumberOf1(int n) {
    
        int cnt = 0;
        // Method 1：  take 32 Every one is associated with 1 Meet each other . Statistics 1 The number of . 
        // 1 Of 32 Base number ： 0000...1 1<<i: By gradually moving left , bring 1 Can and n Every phase of is related to 
       for(int i=0;i<32;i++){
    
           if((n & (1<<i)) != 0){
    
               cnt++;
           }
       }
        return cnt;
    }

Method 2：

Method 2： Gradually n On the right side of the 1 Turn into 0.

public int twoNumberOf1(int n) {
    
        int cnt = 0;
        //  Method 2：  Gradually n On the right side of the 1 Turn into 0.
        // n = n & (n-1);  take n The most the right side 1 Turn into 0 
        while (n != 0){
    
            cnt ++;
            n = n & (n-1);
        }
        return cnt;
    }

Method 3:

Method 3： The digital n Turn into 32 Bit string form .

public int threeNumberOf1(int n) {
    
        int cnt = 0;
        //  Method 3： The digital n Turn into 32 Bit string form .
       String numStr = Integer.toBinaryString(n);
       for(int i=0;i<numStr.length();i++){
    
           if(numStr.charAt(i)=='1'){
    
               cnt++;
           }
       }
        return cnt;
    }