Expression Add Operators Hard Gfg Potd 25 may 2023 @gfg @leetcode @CodeThurst

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In the comment you will find the explaination of the code as well

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[CodeThurst]

Here's a step-by-step explanation of the code:

1)The function find is a recursive helper function that takes several parameters: ind (current index in the string s), s (the input string), target (the target value), ans (a reference to the vector of strings storing the valid expressions), tmp (the current expression being constructed), prev (the previous operand value), and res (the current result of the expression).

2)The base case of the recursion is reached when ind is equal to the size of the input string s. In this case, if the current result res equals the target value, the current expression tmp is added to the ans vector.

3)Inside the recursive function f, a substring st is initialized to store the current digit(s) being considered.

4)The variable curr is used to keep track of the current operand value. It is calculated by multiplying the previous value by 10 and adding the current digit (converted from character to integer).

5)If the current index ind is 0, it means we are at the beginning of the string s. In this case, we recursively call f with the current index incremented by 1 and update the parameters tmp, curr, and res with the current substring st and curr as the new values.

6)If the current index ind is greater than 0, it means we have already processed some digits. In this case, we recursively call f three times:

7)The first call appends the current substring st to tmp with a '+' operator. It updates curr as the new operand value and res as the current result plus the new operand value.
The second call appends the current substring st to tmp with a '-' operator. It updates curr as the new operand value and res as the current result minus the new operand value.
The third call appends the current substring st to tmp with a '*' operator. It updates curr as the new operand value and res as the previous result minus the previous operand value plus the product of the previous operand value and the new operand value.
These recursive calls explore all possible combinations of operators and operands.

8)The main addOperators function initializes an empty vector ans to store the valid expressions and an empty string tmp to construct the current expression.

9)It calls the helper function f with initial values for the parameters: ind as 0, s as the input string, target as the target value, ans as a reference to the empty vector, tmp as the empty string, prev as 0, and res as 0.

10)Finally, it returns the vector ans containing all the valid expressions.

11)The code uses a backtracking approach to explore all possible combinations by recursively generating expressions. It avoids generating expressions with leading zeros by checking the condition if(i > ind && s[ind] == '0') break;. This condition ensures that if the current digit is '0' and it is not the first digit in the current substring, it breaks the loop to avoid generating expressions with



For Multiplication part explaination (audio glitch part)

i+1: This is the updated value of the index ind. It represents the next index to be processed in the string s. By incrementing i by 1, we move to the next digit in the string.
s: This is the input string. It remains the same.
target: This is the target value. It remains the same.
ans: This is the vector of strings storing the valid expressions. It remains the same.
tmp+"*"+st: This is the updated current expression tmp. Here, we concatenate tmp (the current expression constructed so far) with the '' operator and the current substring st. This represents the expression constructed by inserting the '' operator between the previous operand and the current operand.
prev*curr: This is the updated value of the curr operand. It represents the product of the previous operand (prev) and the current operand (curr). It calculates the new operand value after the '*' operator is applied.
res-prev+prev*curr: This is the updated value of the current result res. It calculates the new result by subtracting the previous operand prev and adding the product of the previous operand and the current operand prev*curr.