index.ts

/**
 * # 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
 *
 * ```bash
 * Input: 19
 * Output: true
 * Explanation:
 * 1^2 + 9^2 = 82
 * 8^2 + 2^2 = 68
 * 6^2 + 8^2 = 100
 * 1^2 + 0^2 + 0^2 = 1
 * ```
 *
 * ### Thinkings
 *
 * - 要报所有的推导结果环境，一旦发现已经存在，即除了死循环，立即退出；
 * 一开始以为这题很简单，也没仔细考虑；使用了 Array.reduce() 和 While 控制语句完事；跑测试用例时才发现，第二条用例就没有通过。问题出在时间复杂度上，这里必须对死循环进行处理。
 */
exporttypeSolution=(n: number)=>boolean;

/**
 * @date 2020.06.28 15:18
 * @time
 * @space
 * @runtime 92 ms, faster than 100.00%
 * @memory 36.9 MB, less than 100.00%
 * @runtime_cn 88 ms, faster than 25.00%
 * @memory_cn 35.9 MB, less than 100.00%
 */
exportconstisHappy=(n: number): boolean=>{
letresult: number=n;
constcache=newSet<number>();

consthappify=(n: number): number=>{
letsum=0;
constlen=String(n).length;
for(leti=0;i<len;i++){
sum+=(n%10)**2;
n=(n-n%10)/10;
}
returnsum;
};

while(result!==1){
result=happify(result);
if(cache.has(result)){
returnfalse;
}
cache.add(result);
}
returntrue;
};