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https://leetcode.com/problems/reverse-bits/

Approach 1: Bit by Bit\
Explanation

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public class Solution {
    // you need treat n as an unsigned value
    public int reverseBits(int n) {
        int res=0;
        for(int i=0;i<32;i++){
            res+=n&1;
            n>>>=1;
            if(i<31) res<<=1;
        }
        return res;
    }
}

Approach 3: Mask and Shift

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public class Solution {
    // you need treat n as an unsigned value
    public int reverseBits(int n) {
        n = n >>> 16 | n << 16;
        n = (n & 0xff00ff00) >>> 8 | (n & 0x00ff00ff) << 8;
        n = (n & 0xf0f0f0f0) >>> 4 | (n & 0x0f0f0f0f) << 4;
        n = (n & 0xcccccccc) >>> 2 | (n & 0x33333333) << 2;
        n = (n & 0xaaaaaaaa) >>> 1 | (n & 0x55555555) << 1;
        return n;
    }
}

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