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LeetCode Happy Number 202

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

1^2 + 9^2 = 82
8^2 + 2^2 = 68
6^2 + 8^2 = 100
1^2 + 0^2 + 0^2 = 1


大体意思

题目说的是取任意一个正整数,不断各个数位上数字的平方和,若最终收敛为1,则该数字为happy number,否则程序可能从某个数开始陷入循环。

自己的思路

关键:通过 /% 取 int 各个位的数字;用 set 判重复

public static boolean isHappy(int n) {
Set<Integer> result = new HashSet<>();
int newN = 0;
do {
do {
int end = n % 10;
n = n / 10;
newN += Math.pow(end, 2);
} while (n != 0);

n = newN;
newN = 0;
if (result.contains(n)) {
return false;
} else {
if (n == 1) {
return true;
} else {
result.add(n);
}
}
} while (true);
}

套路:取各个位数字

do {
int end = n % 10;
n = n / 10;
} while (n != 0);