JS gets the random integer value [n,m]

1. Methods to be used:

Math.random: Take a random number greater than or equal to 0 to less than 1;

Math.floor: Rounding down;

Math.ceil: Rounding up;

2. Look at a face question, require a function FN, the parameter is n, you need to return n integers between [2,32]. The first time you write it is as follows:

var fn=function (n) {    var arr=[],num;    for (Var i=0;i<n&&n<32;i++) {        Num=math.floor (math.random () *30+2);        if (Arr.indexof (num) ===-1) {            arr.push (num);        } else{            i--;        }    }    return arr;}; var a=fn (3); Console.log (A.sort ());

Then found that 2 to 32 contains 2 and 32 when there are 31 digits, where I took the wrong only [2,32], and then checked the next random is greater than or equal to 0 less than 1 number, so the downward rounding is always less than 1*30+2 is 32.

And the topic is the requirement contains 2 and 32, I would like to take the whole not to have 32, while the random number of 0 o'clock also has 2, there is the following code:

 var  fn=function   (n) { var  arr=    [],num;  for  (var  i=0;i<n&&n <32;i++ =math.ceil (math.random () *30+2)        ;  if  (Arr.indexof (num) ===-1 else  {i --; }}  return   arr;};  var  a=fn (31 

The

then runs, without the result that the browser is stuck, similar to a dead loop. I think of the next to find myself made a very low-level error, equal to 2 when only the random value of 0, and if the random number is random can not be sure when 0, if not taken to 0, will always i--until 0. Bad luck will run for a long time. So change the code as follows:

 var  fn=function   (n) { var  arr=    [],num;  for  (var  i=0;i<n&&n <32;i++ =math.floor (math.random () *31+2        );  if  (Arr.indexof (num) ===-1 else  {i --; }}  return   arr;};  var  a=fn (31 

Change to rounding down when the value of the random is less than 1/31, the downward rounding is 0, so that 2 is obtained, and the interval is much larger than the probability of just a 0, while the maximum number is always less than 1*31+2, and the next rounding is 32.

Summarize:

A.math.random is the number that takes [0,1];

B. Use the following formula when taking a random integer [Min,max]:

Math.floor (Math.random (). ( max-min+1) +min)

C. Use the following formula when taking a random integer [Min.max]:

Math.floor (Math.random (). ( Max-min) +min)

D. Use the following formula when taking a random integer (Min,max]:

Math.floor (Math.random (). ( Max-min) +min+1)

The above is calculated by the formula (Min,max] that is [Min+1,max] substituting B.

E. Do not use ceil because there is no control over when the Math.random () is 0, as follows:

Math.ceil (Math.random (). ( max-min+1) +min)

It seems to take a value between (Min,max], but it is unclear when it will be taken to Min. Use the random integer to take a downward rounding.

JS gets the random integer value [n,m]