decodeString.java

class Solution {
    public String decodeString(String s) {
        var retVal = new StringBuilder();
        var len = s.length();
        var i = 0;
        while(i < len){
            var chr = s.charAt(i);
            if (Character.isDigit(chr)){
                i = valueOf((i) , s, retVal);
            } else {
                retVal.append(chr);
                i++;
            }
        }
        return retVal.toString();
    }


    private Integer valueOf(int i, String s, StringBuilder result){
        var repStr = getFullRep(i, s);
        var repLen = repStr.length();
        var rep = Integer.valueOf(repStr);
        var of = new StringBuilder();
        var len = s.length();
        var j = ((i+ repLen -1)+2);
        while (j < len){
            var chr = s.charAt(j);
            if (Character.isDigit(chr)){
                j = valueOf(j, s, of);
            } else if (Objects.equals(chr, ']')){
                result.append(compute(rep, of.toString()));
                return (j+1);
            } else {
                of.append(chr);
                j++;
            }
        }
        return (j+1);
    }


    private String compute(int rep, String of){
        var retVal = new StringBuilder();
        for (int i = 0; i < rep; i++){
            retVal.append(of);
        }
        return retVal.toString();
    }

    private String getFullRep(int i, String s){
        var len = s.length();
        var retVal = new StringBuilder();
        while(
            i < len &&
            Character.isDigit(s.charAt(i))
        ){
            retVal.append(s.charAt(i++));
        }
        return retVal.toString();
    }

}

Leetcode Question

Link: https://leetcode.com/problems/decode-string/?envType=study-plan-v2&envId=leetcode-75

Achievement

I write the above code and it beats 100% of the total submissions in terms of runtime with the value of 0 ms.

• The solution uses stack logic.
• Whenever a number is encountered the following string is being pushed to the stack with two values i.e rep- repetitions and of that stores the strings whose repetitions are required