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_338.java
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package com.fishercoder.solutions;
public class _338 {
public static class Solution1 {
//use the most regular method to get it AC'ed first
public int[] countBits(int num) {
int[] ones = new int[num + 1];
for (int i = 0; i <= num; i++) {
ones[i] = countOnes(i);
}
return ones;
}
private int countOnes(int i) {
int ones = 0;
while (i != 0) {
ones++;
i &= (i - 1);
}
return ones;
}
}
private class Solution2 {
/**
* lixx2100's post is cool:https://discuss.leetcode.com/topic/40162/three-line-java-solution
* An easy recurrence for this problem is f[i] = f[i / 2] + i % 2
* and then we'll use bit manipulation to express the above recursion function
* right shift by 1 means to divide by 2
* AND with 1 means to modulo 2
* this is so cool!
*/
public int[] countBits(int num) {
int[] ones = new int[num + 1];
for (int i = 1; i <= num; i++) {
ones[i] = ones[i >> 1] + (i & 1);
}
return ones;
}
}
}