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整数反转
Example1: x = 123, return 321
Example2: x = -123, return -321
@param {number} x
@return {number}

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// 1>
var reverse = function(x) {
    var temp;
    var first = '';
    if(x < 1e+32){
        temp = x.toString();
        if(temp[0] === '-'){
            first = '-';
            temp = temp.substr(1);
        }
        temp = temp.split('');
        temp.reverse();
        temp = temp.join('');
        temp = first + temp;
        return Number(temp);
    }else {
        return 0;
    }
};
// 2>
var reverse = function(x){
    var res = 0;
    if(x < 1e+32){
        while(x > 1 || x < -1){
            res = res * 10 + parseInt(x % 10);
            x /= 10;
        }
        return res;
    }else {
        return 0;
    }
}

console.log(reverse(123));