1 package day20170206;
2 //LeetCode:367. Valid Perfect Square
3 /*
4 Given a positive integer num, write a function which returns True if num is a perfect square else False.
5
6 Note: Do not use any built-in library function such as sqrt.
7
8 Example 1:
9 Input: 16
10 Returns: True
11 Example 2:
12 Input: 14
13 Returns: False
14 */
15 public class isPerfectSquare367 {
16 public static boolean isPerfectSquare(int num) {
17 for(int i=1;i<=num/2+1;i++){
18 if(i*i==num)
19 return true;
20 else if(i*i>num)
21 return false;
22 }
23 return false;
24 }
25 //study1 1+3+5+...+(2n-1)=n^2
26 public static boolean isPerfectSquare2(int num){
27 for(int i=1;num>0;i+=2){
28 num-=i;
29 }
30 return num==0;
31 }
32 //study2 binary search
33 public static boolean isPerfectSquare3(int num){
34 int left=1,right=num;
35 if(num<1)
36 return false;
37 while(left<=right){
38 int mid=left+(right-left)/2;
39 if(mid*mid==num){
40 return true;
41 }
42 else if(mid*mid>num){
43 right=mid-1;
44 }else{
45 left=mid+1;
46 }
47 }
48 return false;
49 }
50 //Newton Method
51 public static boolean isPerfectSquare4(int num){
52 if(num<0)
53 return false;
54 int n=num/2;
55 while(n*n>num){
56 n=(n+num/n)/2;
57 }
58 return n*n==num;
59 }
60
61
62 public static void main(String[] args) {
63 // TODO Auto-generated method stub
64 System.out.println(isPerfectSquare(16));
65 System.out.println(isPerfectSquare(11));
66 System.out.println(isPerfectSquare(1));
67
68 System.out.println(isPerfectSquare2(16));
69 System.out.println(isPerfectSquare2(11));
70 System.out.println(isPerfectSquare2(1));
71
72 System.out.println(isPerfectSquare3(16));
73 System.out.println(isPerfectSquare3(11));
74 System.out.println(isPerfectSquare3(1));
75
76 }
77
78 }
