202. Happy Number

202. Happy Number

Write an algorithm to determine if a number is “happy”.

A happy number is a number defined by the following process: Starting with any positive integer, replace the number by the sum of the squares of its digits, and repeat the process until the number equals 1 (where it will stay), or it loops endlessly in a cycle which does not include 1. Those numbers for which this process ends in 1 are happy numbers.

Example: 19 is a happy number

12 + 92 = 82 82 + 22 = 68 62 + 82 = 100 12 + 02 + 02 = 1

思路： 对这个数字的每个数位求平方和，如果如和为1或者平方和是之前出现过的就不进行求和，根据最后的结果判断是不是一个开心数字。

class Solution { public boolean isHappy(int n) { if (n < 1) { return false; } // 用于保存中间出现的结果 HashSet set = new HashSet<>(32); int tmp; int newN; // n不为1，并且n的值不能重复出现，否则会死循环 while (n != 1 && !set.contains(n)) { set.add(n); newN = 0; while (n > 0) { tmp = n % 10; n /= 10; newN += tmp * tmp; } n = newN; } return n == 1; }}

class Solution { public boolean isHappy(int n) { if(n==2) return false; if(n==1) return true; HashSet set = new HashSet<>(); int sum = 0; while(set.add(sum)) { sum = helper(n); n = sum; } if(sum==1) return true; return false; } private int helper(int num) { int sum=0; while(num > 0) { int temp = num%10; if(temp>0) sum=sum+temp*temp; num=num/10; } return sum; }}

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