zoukankan      html  css  js  c++  java
  • 190. Reverse Bits

    Reverse bits of a given 32 bits unsigned integer.

    Example 1:

    Input: 00000010100101000001111010011100
    Output: 00111001011110000010100101000000
    Explanation: The input binary string 00000010100101000001111010011100 represents the unsigned integer 43261596, so return 964176192 which its binary representation is 00111001011110000010100101000000.
    

    Example 2:

    Input: 11111111111111111111111111111101
    Output: 10111111111111111111111111111111
    Explanation: The input binary string 11111111111111111111111111111101 represents the unsigned integer 4294967293, so return 3221225471 which its binary representation is 10101111110010110010011101101001.

    Note:

    • Note that in some languages such as Java, there is no unsigned integer type. In this case, both input and output will be given as signed integer type and should not affect your implementation, as the internal binary representation of the integer is the same whether it is signed or unsigned.
    • In Java, the compiler represents the signed integers using 2's complement notation. Therefore, in Example 2 above the input represents the signed integer -3 and the output represents the signed integer -1073741825.

    Follow up:

    If this function is called many times, how would you optimize it?

    e.g.
    n = b7 1 b5 b4 b3 b2 0 b0
    0 0 0 0 0 0 1 0 1 << i (i = 1)
    0 1 0 0 0 0 0 0 1 << j (j = 6)
    xor 0 1 0 0 0 0 1 0 bit_mask = ( (1 << i) | (1 << j) )
    b7 0 b5 b4 b3 b2 1 b0 n ^ bit_mask
    b7 ~b6 b5 b4 b3 b2 ~b1 b0

    time = O(1), space = O(1)

    public class Solution {
        // you need treat n as an unsigned value
        public int reverseBits(int n) {
            int i = 0, j = 31;
            while(i < j) {
                n = reverseBitPair(n, i++, j--);
            }
            return n;
        }
        
        private int reverseBitPair(int n, int i, int j) {
            int leftBit = (n >> i) & 1;
            int rightBit = (n >> j) & 1;
            if(leftBit != rightBit) {
                n ^= ((1 << i) | (1 << j));
            }
            return n;
        }
    }
  • 相关阅读:
    预览图片功能 直接复制就OK
    记录:express返回自定义http状态吗
    Git tag 给当前分支打标签
    css双飞翼和圣杯布局
    简单模拟MVVM数据双向绑定
    JS的自定义事件(观察者模式)
    js模拟触发事件
    QueryString和BASE64
    WebResource.axd文件的配置和使用
    处理json中的异常字符
  • 原文地址:https://www.cnblogs.com/fatttcat/p/11404502.html
Copyright © 2011-2022 走看看