Create 592. Fraction Addition and Subtraction (#565)

592. Fraction Addition and Subtraction

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+class Solution {
+    struct frac_t {
+        int above;
+        int below;
+    };
+
+    void getFracs(vector<frac_t> &fracs, string &expr) {
+        int N = expr.length();
+        int idx = 0;
+        int sign = 1;
+
+        frac_t frac;
+        int digit = 0;
+        while (idx < N) {
+            if (isdigit(expr[idx])) {
+                digit = digit * 10 + (expr[idx] - '0');
+            }
+            else if (expr[idx] == '/') {
+                frac.above = sign * digit;
+                digit = 0;
+                sign = 1;
+            }
+            else {
+                frac.below = sign * digit;
+                fracs.push_back(frac);
+
+                digit = 0;
+                sign = expr[idx] == '+' ? 1 : -1;
+            }
+
+            ++idx;
+        }
+
+        /* Add last frac to fracs */
+        frac.below = sign * digit;
+        fracs.push_back(frac);
+    }
+
+    void addFrac(frac_t &result, frac_t toAdd) {
+        if (result.below == 0) {
+            result = toAdd;
+            return ;
+        }
+
+        /* Get the least common multiple */
+        int below_lcm = lcm(result.below, toAdd.below);
+        result.above *= below_lcm / result.below;
+        toAdd.above *= below_lcm / toAdd.below;
+
+        /* Update result */
+        result.above += toAdd.above;
+        result.below = below_lcm;
+    }
+
+public:
+    string fractionAddition(string expression) {
+        vector<frac_t> fracs;
+        getFracs(fracs, expression);
+
+        /* Frac Addition */
+        frac_t result(0, 0);
+        for (frac_t frac : fracs) {
+            addFrac(result, frac);
+        }
+
+        /* Simplify the result */
+        if (result.above == 0) {
+            return "0/1";
+        }
+
+        /* Greatest common divisor */ 
+        int result_gcd = gcd(result.above, result.below);
+        result.above /= result_gcd;
+        result.below /= result_gcd;
+
+        return to_string(result.above) + "/" + to_string(result.below);
+    }
+};