> For the complete documentation index, see [llms.txt](https://mayanktyagi3111.gitbook.io/interview-prep/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://mayanktyagi3111.gitbook.io/interview-prep/two-pointers/form-minimum-number-from-given-sequence.md).

# Form minimum number from given sequence

Given a pattern containing only I’s and D’s. **I** for increasing and **D** for decreasing. Devise an algorithm to print the minimum number following that pattern. Digits from 1-9 and digits can’t repeat.

**Examples:**

```
   Input: D        Output: 21
   Input: I        Output: 12
   Input: DD       Output: 321
   Input: II       Output: 123
   Input: DIDI     Output: 21435
   Input: IIDDD    Output: 126543
   Input: DDIDDIID Output: 321654798 
```

```java
/**
 * When first 'I' comes in input is the place where we have to print 1 and for
 * all the 'D' before 'I' we print grater than 1 in series
 * 
 * Like if we have DDID First i comes at 3rd place so we print 1 at 3rd place
 * 
 * So it will be like 321 And in code firstly we find max num is length of
 * string + 1 So here we have 5 and we already print 321 now we print remaining
 * from 5 to grater than 3 so it will be like 32154 and it's the output
 */
public class solution {
    static String getMinNumberForPattern(String str) {
        int n = str.length();
        if (n >= 9)
            return "-1";

        char result[] = new char[n + 1];
        int lastI = -1;
        int currentValueToPut = 1;
        // O(n) -> Every character is traversed twice
        for (int i = 0; i <= n; i++) {
            // Find 'I' OR END of string
            if (i == n || str.charAt(i) == 'I') {
                // Putting values in increasing order (in reverse) to get decreasing order in
                // correct direction
                for (int j = i; j > lastI; j--) {
                    char digit = (char) (currentValueToPut + '0');
                    result[j] = digit;
                    currentValueToPut++;
                }
                lastI = i;
            }
        }
        return new String(result);
    }

    public static void main(String[] args) {
        String inputs[] = { "IDID", "I", "DD", "II", "DIDI", "IIDDD", "DDIDDIID" };
        for (String input : inputs) {
            System.out.println(input + " -> " + getMinNumberForPattern(input));
        }
    }
}
```


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