leetcode---Power of Two---lower_bound,upper_bound,binary_search

Given an integer, write a function to determine if it is a power of two.

Credits:
Special thanks to @jianchao.li.fighter for adding this problem and creating all test cases.

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class Solution {public:    vector<int> powTwo;    bool isPowerOfTwo(int n) {        vector<int> powTwo;            int i;        for(i=0; i<31; i++)        {            int a = (1 << i);            powTwo.push_back(a);        }        vector<int>::iterator l, r;        l = lower_bound(powTwo.begin(), powTwo.end(), n);        r = upper_bound(powTwo.begin(), powTwo.end(), n);        if(l == r-1)            return true;        else            return false;    }};

class Solution {public:    vector<int> powTwo;    bool isPowerOfTwo(int n) {        vector<int> powTwo;            int i;        for(i=0; i<31; i++)        {            int a = (1 << i);            powTwo.push_back(a);        }        int m = binary_search(powTwo.begin(), powTwo.end(), n);        if(m == 1)            return true;        else            return false;    }};