feat : added Solution.js for MissingDigit

Solution.js

@@ -1 +1,52 @@
 // Write your code here
+class FixEquation {
+    constructor(a) {
+        this.equation = a;
+    }
+    findMissingDigit() {
+        const eqn = this.equation.split(' ');
+        const A = eqn[0], B = eqn[2], C = eqn[4], D = eqn[6];
+        let mark, result;
+        if (A.includes('?')) {
+            result = (parseInt(D) - parseInt(C)) / parseInt(B);
+            mark = A;
+        }
+        else if (B.includes('?')) {
+            result = (parseInt(D) - parseInt(C)) / parseInt(A);
+            mark = B;
+        }
+        else if (C.includes('?')) {
+            result = parseInt(D) - parseInt(A) * parseInt(B);
+            mark = C;
+        }
+        else if (D.includes('?')) {
+            result = parseInt(A) * parseInt(B) + parseInt(C);
+            mark = D;
+        }
+        if (result < 0 || !Number.isInteger(result)) {
+            return -1;
+        }
+        result = result.toString();
+        if (result.length !== mark.length) {
+            return -1;
+        }
+        // console.log(mark)
+        let final_ans;
+        for (let i = 0; i < result.length; i++) {
+            // console.log(mark[i])
+            if (result[i] !== mark[i] && mark[i] !== '?') {
+                return -1;
+            }
+            if (mark[i] === '?') {
+                // console.log("yo")
+                final_ans =  parseInt(result[i]);
+            }
+        }
+        return final_ans;
+        // return -1;
+
+    }
+}
+var test = new FixEquation('2 * ? + 1 = 15');
+var fun = test.findMissingDigit();
+console.log("Missing Digit is " + fun);