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202. Happy Number.cpp
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202. Happy Number.cpp
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/* 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 */
//code
class Solution {
public:
int solve(int n){
//if the number is a single digit number then return the number
if(n>=1 && n<=9){
return n;
}
//otherwise perform the following operation
int sum = 0;
while(n>0){
int rem = n%10;
sum += rem*rem;
n = n/10;
}
int ans = solve(sum);
return ans;
}
bool isHappy(int n) {
int res = solve(n);
if(res == 1 || res ==7)return true; //only 1 and 7 are happy numbers from digits 1 to 9
return false;
}
};