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leetcode_java/src/main/java/LeetCodeJava/Math/CountingBits.java
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| @@ -0,0 +1,60 @@ | ||
| package LeetCodeJava.Math; | ||
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| // https://leetcode.com/problems/counting-bits/ | ||
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| public class CountingBits { | ||
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| // V0 | ||
| // IDEA : MATH | ||
| public int[] countBits(int n) { | ||
| /** NOTE !!! we init ans as below */ | ||
| int[] ans = new int[n+1]; | ||
| for (int x = 0; x < n+1; x++){ | ||
| // https://stackoverflow.com/questions/2406432/converting-an-int-to-a-binary-string-representation-in-java | ||
| String binary = Integer.toBinaryString(x); | ||
| ans[x] = countElement(binary, '1'); | ||
| } | ||
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| return ans; | ||
| } | ||
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| // https://www.baeldung.com/java-count-chars | ||
| private int countElement(String s, char x){ | ||
| int count = 0; | ||
| for (int i = 0; i < s.length(); i++){ | ||
| if (s.charAt(i) == x){ | ||
| count += 1; | ||
| } | ||
| } | ||
| return count; | ||
| } | ||
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| // V1 | ||
| // https://leetcode.com/problems/counting-bits/solutions/3987279/java-solution-using-right-shift-operator/ | ||
| public int countOnes(int n) { | ||
| int count = 0; | ||
| while(n != 0) { | ||
| count += (n&1); | ||
| n = n>>1; | ||
| } | ||
| return count; | ||
| } | ||
| public int[] countBits_1(int n) { | ||
| int ans[] = new int[n+1]; | ||
| ans[0] = 0; | ||
| for(int i=1; i<ans.length; i++) { | ||
| ans[i] = countOnes(i); | ||
| } | ||
| return ans; | ||
| } | ||
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| // V2 | ||
| // IDEA : BIT OP | ||
| // https://leetcode.com/problems/counting-bits/solutions/79539/three-line-java-solution/ | ||
| public int[] countBits_2(int num) { | ||
| int[] f = new int[num + 1]; | ||
| for (int i=1; i<=num; i++) f[i] = f[i >> 1] + (i & 1); | ||
| return f; | ||
| } | ||
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| } |