Lecture 160:-Decode String

The problem of decoding a string involves converting a string that has been encoded using a specific pattern back to its original form. The encoding pattern typically involves specifying a number followed by a string within square brackets, indicating that the string within the brackets should be repeated the specified number of times.

For example, the encoded string "3[a2[bc]]" represents "abcbcabcbcabcbc".

To decode such an encoded string, you can use a stack to keep track of the characters and numbers. Here's an approach to solve the "Decode String" problem:

1. Iterate through each character of the encoded string.
2. If the character is a digit, accumulate the digit to form the repeat count.
3. If the character is an opening square bracket [, push the current repeat count and the current decoded string onto the stack.
4. If the character is a closing square bracket ], pop the repeat count and the previous decoded string from the stack. Append the current decoded string repeated by the repeat count to the previous decoded string.
5. If the character is not a digit or a square bracket, append it to the current decoded string.
6. After iterating through the entire string, the stack should contain the final decoded string.

Here's a C++ implementation of the "Decode String" problem:

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#include <iostream> #include <stack> std::string decodeString(const std::string& s) { std::stack<int> numStack; std::stack<std::string> strStack; std::string currStr; int currNum = 0; for (char ch : s) { if (isdigit(ch)) { currNum = currNum * 10 + (ch - '0'); } else if (ch == '[') { numStack.push(currNum); strStack.push(currStr); currNum = 0; currStr.clear(); } else if (ch == ']') { int repeat = numStack.top(); numStack.pop(); std::string prevStr = strStack.top(); strStack.pop(); for (int i = 0; i < repeat; ++i) { prevStr += currStr; } currStr = prevStr; } else { currStr += ch; } } return currStr; } int main() { std::string encoded = "3[a2[bc]]"; std::string decoded = decodeString(encoded); std::cout << "Encoded string: " << encoded << std::endl; std::cout << "Decoded string: " << decoded << std::endl; return 0; }

In this example, the decodeString function decodes the encoded string using the approach described earlier. The main function demonstrates how to use this function for a specific input.

For the input "3[a2[bc]]", the output will be:

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Encoded string: 3[a2[bc]] Decoded string: abcbcabcbcabcbc

This demonstrates the process of decoding an encoded string back to its original form.