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徐长贺/Leetcode

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_191.java 1.96 KB
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stevesun 提交于 8年前 . refactor 191
package com.fishercoder.solutions;
/**
* 191. Number of 1 Bits
*
* Write a function that takes an unsigned integer and returns the number of ’1' bits it has (also known as the Hamming weight).
* For example, the 32-bit integer ’11' has binary representation 00000000000000000000000000001011, so the function should return 3.*/
public class _191 {
public static class Solution1 {
/**Doing bitwise AND operation between n and n-1 will always flip the least significant 1 bit in n to zero
example run for the above editorial solution: input 5, n will be 5&4 and becomes 4,
then in the next run, n will become 4&3 which is 0, thus exit the while loop.*/
public int hammingWeight(int n) {
int bits = 0;
while (n != 0) {
bits++;
n &= (n - 1);
}
return bits;
}
}
public static class Solution2 {
public int hammingWeight(int n) {
int bits = 0;
int mask = 1;
for (int i = 0; i < 32; i++) {
if ((n & mask) != 0) {
bits++;
}
mask <<= 1;
}
return bits;
}
}
public static class Solution3 {
public int hammingWeight(int n) {
int bits = 0;
for (int i = 0; i < 32; i++) {
if ((n & 1) == 1) {
bits++;
}
if (n == 0) {
return bits;
}
/**must use unsigned right shift operator since the problem says this is an unsigned value*/
n >>>= 1;
}
return bits;
}
}
public static class Solution4 {
public int hammingWeight(int n) {
int bits = 0;
for (int i = 0; i < 32; i++) {
bits += n & 1;
n >>>= 1;
}
return bits;
}
}
}
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