Welcome to Subscribe On Youtube

202. Happy Number

Description

Write an algorithm to determine if a number n 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.
• 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.

Return true if n is a happy number, and false if not.

 

Example 1:

Input: n = 19
Output: true
Explanation:
12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1

Example 2:

Input: n = 2
Output: false

 

Constraints:

• 1 <= n <= 231 - 1

Solutions

• Java
• C++
• Python
• Go
• TypeScript
• RenderScript

• class Solution {
      public boolean isHappy(int n) {
          int slow = n, fast = next(n);
          while (slow != fast) {
              slow = next(slow);
              fast = next(next(fast));
          }
          return slow == 1;
      }
  
      private int next(int x) {
          int y = 0;
          for (; x > 0; x /= 10) {
              y += (x % 10) * (x % 10);
          }
          return y;
      }
  }
  

• class Solution {
  public:
      bool isHappy(int n) {
          auto next = [](int x) {
              int y = 0;
              for (; x; x /= 10) {
                  y += pow(x % 10, 2);
              }
              return y;
          };
          int slow = n, fast = next(n);
          while (slow != fast) {
              slow = next(slow);
              fast = next(next(fast));
          }
          return slow == 1;
      }
  };
  

• class Solution:
      def isHappy(self, n: int) -> bool:
          def next(x):
              y = 0
              while x:
                  x, v = divmod(x, 10)
                  y += v * v
              return y
  
          slow, fast = n, next(n)
          while slow != fast:
              slow, fast = next(slow), next(next(fast))
          return slow == 1
  
  

• func isHappy(n int) bool {
  	next := func(x int) (y int) {
  		for ; x > 0; x /= 10 {
  			y += (x % 10) * (x % 10)
  		}
  		return
  	}
  	slow, fast := n, next(n)
  	for slow != fast {
  		slow = next(slow)
  		fast = next(next(fast))
  	}
  	return slow == 1
  }
  

• function isHappy(n: number): boolean {
      const getNext = (n: number) => {
          let res = 0;
          while (n !== 0) {
              res += (n % 10) ** 2;
              n = Math.floor(n / 10);
          }
          return res;
      };
  
      let slow = n;
      let fast = getNext(n);
      while (slow !== fast) {
          slow = getNext(slow);
          fast = getNext(getNext(fast));
      }
      return fast === 1;
  }
  
  

• impl Solution {
      pub fn is_happy(n: i32) -> bool {
          let get_next = |mut n: i32| {
              let mut res = 0;
              while n != 0 {
                  res += (n % 10).pow(2);
                  n /= 10;
              }
              res
          };
          let mut slow = n;
          let mut fast = get_next(n);
          while slow != fast {
              slow = get_next(slow);
              fast = get_next(get_next(fast));
          }
          slow == 1
      }
  }
  
  

All Problems

All Solutions