• 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 ;
        }
    }
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  • 原文地址:https://www.cnblogs.com/xiaoba1203/p/6612505.html
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