45 lines
1.2 KiB
C++
45 lines
1.2 KiB
C++
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// Source : https://leetcode.com/problems/power-of-two/
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// Author : Hao Chen
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// Date : 2015-07-16
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/**********************************************************************************
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*
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* Given an integer, write a function to determine if it is a power of two.
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*
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* Credits:Special thanks to @jianchao.li.fighter for adding this problem and creating
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* all test cases.
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*
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*
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*
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**********************************************************************************/
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class Solution {
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public:
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// count the number fo bits 1, if it only has one, then return true
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bool isPowerOfTwo01(int n) {
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int cnt = 0; //num of bits 1
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for(; n>0; n>>=1){
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if ( n & 1 ) {
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cnt++;
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if (cnt>1) return false;
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}
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}
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return cnt==1;
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}
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//we notice: 2^n - 1 always be 1111111...
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//so, (2^n) & (2^n-1) always be zero
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bool isPowerOfTwo02(int n) {
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return n<=0 ? false : (n & (n-1)) == 0;
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}
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bool isPowerOfTwo(int n) {
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if (random()%2){
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return isPowerOfTwo02(n);
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}
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return isPowerOfTwo01(n);
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}
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};
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