137. Single Number II leetcode

singleNumber.ts

    function singleNumber(nums: number[]):number {
    let map=new Map<number,number>()
    for (const num of nums) {
        if (map.has(num)) {
            const nextCount = map.get(num) as number + 1
            if (nextCount === 3) {
                map.delete(num)
            } else {
                map.set(num, nextCount)
            }
        } else {
            map.set(num, 1)
        }
    }
    return map.keys().next().value
  }