137. 只出现一次的数字 II

/** 方法一：哈希表
 * @param {number[]} nums
 * @return {number}
 */
var singleNumber = function(nums) {
    let map = new Map();
    let res;
    for(let num of nums){
        freq.set(num, (freq.get(num)||0) +1 )
    }
    for(let [m,c] of map){
        if(c==1){
            res = m;
            break;
        }
    }
    return res;
}; 


/** 方法二：依次确定每一个二进制位
 * @param {number[]} nums
 * @return {number}
 */
 var singleNumber = function(nums) {
    let res = 0;
    for(let i = 0;i<32;i++){
        let total = 0;
        for(let num of nums){
            total += (num>>i)&1;
        }
        
        if(total%3 != 0){
            res |= 1<<i;
        }
    }
    return res;
}; 
let nums = [2,2,3,2]
console.log(nums, singleNumber(nums))


nums =[0,1,0,1,0,1,99]
console.log(nums, singleNumber(nums))


/** 状态机2
 * @param {number[]} nums
 * @return {number}
 */
 var singleNumber = function(nums) {
    let a = 0,b=0;
    for(let num of nums){
        let aNext = ~a&b&num|a&~b&~num;
        let bNext = ~a&~b&num|~a&b&~num;
        a = aNext;
        b = bNext;
    }
    return b;
};