Next greater element

Given a number n, find the smallest number that has same set of digits as n and is greater than n. If x is the greatest possible number with its set of digits, then print “not possible”.

examples:
input: 1111
output: not possible

inout: 1234
output: 1243

input: 12345765
output: 12346557

Solution:
Assume the input is a int[] num.
1. Scan from the end, and find the 1st position i, where num[i] < num[i+1]. Let i be smallPos.
2. Scan from the end again, find the 1st position j, where num[smallPos] < num[j]. Let j be largePos.
3. Do exchange between num[smallPos] and num[largePos].
4. Do exchange from num[smallPos+1] and num[num.length – 1], num[smallPos+2] and num[num.length – 2], num[smallPos+3] and num[num.length – 3] and so on.
This time, I used node.js to solve this problem.
The visiting format is http://allenlipeng47.com:3000/nge/{input}
For example: http://allenlipeng47.com:3000/nge/66355331
There are 2 files: app.js and npe.js:
node/app.js
node/mymodule/npe.js

npe.js:

1. /*
2. Given a number n, find the smallest number that has same set of digits as n and is greater than n. If x is the greatest possible number with its set of digits, then print “not possible”.
3. The input num is a char array type.
4. */
5. function npe(num){
6.     num = num.split(”);
7.     if(num.length==1){
8.         return ‘not possible’;
9.     }
10.     var smallPos = num.length – 2;
11.     while(smallPos >=0 && num[smallPos] >= num[smallPos+1]){
12.         smallPos–;
13.     }
14.     if(smallPos < 0){
15.         return ‘not possible’;
16.     }
17.     var largePos = num.length – 1;
18.     while(num[largePos] <= num[smallPos]){
19.         largePos–;
20.     }
21.     var tmp = num[smallPos];
22.     num[smallPos] = num[largePos];
23.     num[largePos] = tmp;
24.     for(largePos = num.length – 1, ++smallPos; smallPos < largePos; smallPos++, largePos–){
25.         var tmp = num[smallPos];
26.         num[smallPos] = num[largePos];
27.         num[largePos] = tmp;
28.     }
29.     num = num.join(”);
30.     return num;
31. }
32. module.exports = npe;

app.js

1. var express = require(‘express’)
2. var app = express();
3. app.get(‘/nge/:id’, function (req, res){
4.     var npe = require(‘./mymodule/npe.js’);
5.     var result = npe(req.params.id);
6.     res.send(result);
7. })
8. app.get(‘*’, function (req, res){
9.     res.send(‘Welcome to Li Peng\’s node.js!’);
10. })
11. var server = app.listen(3000, function(){
12.     var host = server.address().address
13.     var port = server.address().port
14. });