Feat: Added solution for the assignment

Solution.js

@@ -1 +1,157 @@
-// Write your code here
+// 
+// Solution by: Akshath Kaushal
+// GitHub: https://github.com/akshathkaushal
+// LinkedIn: www.linkedin.com/in/akshath-kaushal-08277817b
+// 
+
+
+// object class
+class FixEquation {
+
+    findMissingDigit(str) {
+        // str is of the form A * B + C = D
+        // in this either A, B, C or D has a '?' that has to be found
+
+
+        // step 1: separate the numeric values from the equation
+        let values = this.separateValues(str);
+        let mul1=values[0], mul2=values[1], add=values[2], res=values[3];
+
+        // step 2: find position (1/2/3/4) of the number(A/B/C/D) containing a '?'  
+        let qnmarkPos = this.findQuestionMark(mul1, mul2, add, res);
+
+        // step 3: based on the position of the found number, calculate the actual value of that number
+        let temp = -1, ans=-1, arg2="";
+        if(qnmarkPos==1){ // '?' is found in A
+            temp = (parseFloat(res) - parseFloat(add))/parseFloat(mul2);
+            ans = parseInt(temp);
+            arg2=mul1;
+        }
+        else if(qnmarkPos==2){ // '?' is found in B
+            temp = (parseFloat(res) - parseFloat(add))/parseFloat(mul1);
+            ans = parseInt(temp);
+            arg2=mul2;
+        }
+        else if(qnmarkPos==3){ // '?' is found in C
+            temp = parseFloat(res) - (parseFloat(mul2)*parseFloat(mul1));
+            ans = parseInt(temp);
+            arg2=add;
+        }
+        else if(qnmarkPos==4){ // '?' is found in D
+            temp = parseFloat(mul1)*parseFloat(mul2) + parseFloat(add);
+            ans = parseInt(temp);
+            arg2=res;            
+        }
+
+        // step 4: return the digit that should replace the '?' 
+        if(ans < 0 || temp - ans != 0) { // if the ans is negative or not a whole number
+            return -1;
+        }
+        return this.findDigit(ans.toString(), arg2);
+    }
+
+    // ================= helper functions ================= //
+
+    //  
+    // this function separates the differnt numbers by iterating through the string
+    // return type: a list of the numbers as strings
+    // 
+    separateValues(str){
+
+        let mul1="", mul2="", add="", res="";
+        let i = 0, sz = str.length;
+
+        while(str[i] != '*'){
+            if(str[i]!=' ') mul1+=str[i];
+            i++;
+        }
+        i+=2;
+        while(str[i] != '+'){
+            if(str[i]!=' ') mul2+=str[i];
+            i++;
+        }
+        i+=2;
+        while(str[i] != '='){
+            if(str[i]!=' ') add+=str[i];
+            i++;
+        }
+        i+=2;
+        while(i<sz) {
+            res+=str[i];
+            i++;
+        }
+
+        return [mul1, mul2, add, res];
+    }
+
+    //
+    // this function finds which number (A/B/C/D) contains a '?'
+    // if A contains a '?', 1 is returned
+    // if B contains a '?', 2 is returned
+    // if C contains a '?', 3 is returned
+    // if D contains a '?', 4 is returned
+    // if a '?' is not found, -1 is returned
+    // 
+    findQuestionMark(mul1, mul2, add, res){
+        let order=-1;
+        if(this.checkString(mul1)) order=1;
+        else if(this.checkString(mul2)) order=2;
+        else if(this.checkString(add)) order=3;
+        else if(this.checkString(res)) order=4;
+        return order;
+    }
+
+    //
+    // this function checks if the string str (argument) contains a '?' or not
+    // if '?' is preesent, true is returned, else false is returned.
+    // 
+    checkString(str){
+        let i=0, sz = str.length;
+        for(i=0;i<sz;i++){
+            if(str[i] == '?') return true;
+        }
+        return false;
+    }
+
+    // 
+    // this functions iterates str (argument) and checks the position of '?'
+    // then it returns the corresponding digit at the designated value of '?'
+    // 
+    findDigit(ans, str){
+        if(ans.length != str.length) {
+            return -1; // leading zero or non-whole number case
+        }
+        let itr=0, ret;
+
+        while(itr<ans.length){
+            if(str[itr]=='?') ret = parseInt(ans[itr]);
+            else if(str[itr] != ans[itr]) { // if apart from the '?' some other digit doesn't match
+                return -1;
+            }
+            itr++;
+        }
+        return ret;
+    }
+
+}
+
+
+// driver code
+let listOfEquations = [
+    "42 * 47 + 2 = 1?76", 
+    "4? * 47 + 2 = 1976", 
+    "42 * ?7 + 2 = 1976", 
+    "42 * ?47 + 2 = 1976", 
+    "2 * 12? + 2 = 247"
+];
+
+let i=0;
+let fixedEquationResponse = new FixEquation();
+
+for(i=0;i<listOfEquations.length;i++){
+    let equation = listOfEquations[i];
+    let response = fixedEquationResponse.findMissingDigit(equation);
+
+    console.log("Equation: " + equation);
+    console.log("Returns: " + response);
+}