Number of 1 in binary

Title Description: Implement a function, enter an integer, and output the number of 1 in the binary representation.

For example: 9 indicates that binary is 1001, and 2 bits are 1. So if you enter 9, the function outputs 2.

First look at a wrong solution: 650) this.width=650; "src=" Http://img.baidu.com/hi/jx2/j_0015.gif "alt=" J_0015.gif "/>

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int NumberOf1 (int n) {int count = 0;        while (n) {if (n & 1) count + +;    n = n >> 1; } return count;}

Note: when using multiplication or division operations, use shift operations as much as possible instead, because the efficiency of the shift operation is much higher than the multiplication method!

The problem with this solution is that you enter a positive number, and the result is fine, but what happens if you enter a negative number?

We know that the highest number of negative binary is 1, when the right shift operation, the highest bit to fill the sign bit is 1, so each right shift one, the highest bit of 1, the final figure will become 0xFFFFFFFF, and into a dead loop.

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Conventional Solutions

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int numberof1_solution1 (int n) {int count = 0;    unsigned int flag = 1;        while (flag) {if (n & Flag) Count + +;    Flag = Flag << 1; } return count;}

The number of loops in this solution is equal to the number of digits in the integer binary, and 32-bit integers need to be cycled 32 times.

High-efficiency solution

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int NumberOf1 (int n) {int count = 0;        while (n) {+ + count;    n = (n-1) & N; } return count;}

The solution has several 1 in integers and only needs to be looped several times.

Related Topics 650) this.width=650; "src=" Http://img.baidu.com/hi/jx2/j_0028.gif "alt=" J_0028.gif "/>

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Number of 1 in binary