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leetcode 202. Happy Number 判断一个数是否是“Happy Number” ---------- java
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
按照上述规则,如果能够满足上述规则得数那么就是一个Happy Number
用一个set来记录已经出现过得数,避免死循环
public class Solution { public boolean isHappy(int n) { Set<Integer> set = new HashSet(); return isHappyNum(n, set); } public boolean isHappyNum(int n, Set set){ if (set.contains(n)){ return false; } set.add(n); int num = 0; while (n != 0){ num += (n % 10) * (n % 10); n /= 10; } if (num == 1){ return true; } else { return isHappyNum(num, set); } } }
2、使用O(1)的空间复杂度。很巧妙,如果会出现循环的情况,那么x和y一定会相遇,也就一定会跳出循环。
public class Solution { public boolean isHappy(int n) { int x = n; int y = n; while(x>1){ x = cal(x) ; if(x==1) return true ; y = cal(cal(y)); if(y==1) return true ; if(x==y) return false; } return true ; } public int cal(int n){ int x = n; int s = 0; while(x>0){ s = s+(x%10)*(x%10); x = x/10; } return s ; } }
leetcode 202. Happy Number 判断一个数是否是“Happy Number” ---------- java
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