标签：class strong function ica span begin wan which use
Given a positive integer num, write a function which returns True if num is a perfect square else False.
Note: Do not use any built-in library function such as sqrt.
Example 1:
Input: 16
Returns: True
Solution 1: use BST,O(logn)
1 class Solution { 2 public: 3 bool isPerfectSquare(int num) { 4 if (num==1) return true; 5 int begin=0,end=num; 6 while (begin<end-1){ 7 long long mid=(begin+end)/2; 8 if (mid*mid==num) return true; 9 if (mid*mid<num) begin=mid; 10 if (mid*mid>num) end=mid; 11 } 12 return false; 13 } 14 };
Solution 2: Newton‘s method, http://blog.csdn.net/wangxiaojun911/article/details/18203333
1 class Solution { 2 public: 3 bool isPerfectSquare(int num) { 4 long long x=num; 5 while(x*x>num) x=(x+num/x)/2; 6 return x*x==num; 7 } 8 };
Soulution 3: q_math.c special method, O(1)
标签：class strong function ica span begin wan which use
原文地址：http://www.cnblogs.com/anghostcici/p/6821265.html
