add 592

fishercoder1534 · fishercoder1534 · commit 5c7972b68321 · 2017-05-23T11:04:09.000-07:00
diff --git a/README.md b/README.md
@@ -22,6 +22,7 @@ Your ideas/fixes/algorithms are more than welcome!
 |-----|----------------|---------------|---------------|---------------|-------------|--------------|-----
 |594|[Longest Harmonious Subsequence](https://leetcode.com/problems/longest-harmonious-subsequence/)|[Solution](../master/src/main/java/com/stevesun/solutions/_594.java) | O(n) |O(n) | Easy | Array, HashMap
 |593|[Valid Square](https://leetcode.com/problems/valid-square/)|[Solution](../master/src/main/java/com/stevesun/solutions/_593.java) | O(1) |O(1) | Medium | Math
+|592|[Fraction Addition and Subtraction](https://leetcode.com/problems/fraction-addition-and-subtraction/)|[Solution](../master/src/main/java/com/stevesun/solutions/_592.java) | O(nlogx) |O(n) | Medium | Math
 |583|[Delete Operation for Two Strings](https://leetcode.com/problems/delete-operation-for-two-strings/)|[Solution](../master/src/main/java/com/stevesun/solutions/_583.java) | O(m*n) |O(m*n) could be optimized to O(n) | Medium | DP
 |582|[Kill Process](https://leetcode.com/problems/kill-process/)|[Solution](../master/src/main/java/com/stevesun/solutions/_582.java) | O(n) |O(h) | Medium | Stack
 |581|[Shortest Unsorted Continuous Subarray](https://leetcode.com/problems/shortest-unsorted-continuous-subarray/)|[Solution](../master/src/main/java/com/stevesun/solutions/_581.java) | O(n) |O(1) | Easy | Array, Sort
diff --git a/src/main/java/com/stevesun/solutions/_592.java b/src/main/java/com/stevesun/solutions/_592.java
@@ -0,0 +1,92 @@
+package com.stevesun.solutions;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * 592. Fraction Addition and Subtraction
+ *
+ * Given a string representing an expression of fraction addition and subtraction,
+ * you need to return the calculation result in string format.
+ * The final result should be irreducible fraction.
+ * If your final result is an integer,
+ * say 2, you need to change it to the format of fraction that has denominator 1.
+ * So in this case, 2 should be converted to 2/1.
+
+ Example 1:
+ Input:"-1/2+1/2"
+ Output: "0/1"
+
+ Example 2:
+ Input:"-1/2+1/2+1/3"
+ Output: "1/3"
+
+ Example 3:
+ Input:"1/3-1/2"
+ Output: "-1/6"
+
+ Example 4:
+ Input:"5/3+1/3"
+ Output: "2/1"
+
+ Note:
+ The input string only contains '0' to '9', '/', '+' and '-'. So does the output.
+ Each fraction (input and output) has format ±numerator/denominator.
+ If the first input fraction or the output is positive, then '+' will be omitted.
+ The input only contains valid irreducible fractions,
+ where the numerator and denominator of each fraction will always be in the range [1,10].
+ If the denominator is 1, it means this fraction is actually an integer in a fraction format defined above.
+ The number of given fractions will be in the range [1,10].
+ The numerator and denominator of the final result are guaranteed to be valid and in the range of 32-bit int.
+ */
+public class _592 {
+
+    /**Credit: https://discuss.leetcode.com/topic/89993/java-solution-fraction-addition-and-gcd*/
+    public String fractionAddition(String expression) {
+        List<String> nums = new ArrayList<>();
+        int i = 0;
+        int j = 0;
+        while (j <= expression.length()) {
+            if (j == expression.length() || j != i && (expression.charAt(j) == '-' || expression.charAt(j) == '+')) {
+                if (expression.charAt(i) == '+') {
+                    nums.add(expression.substring(i+1, j));
+                } else {
+                    nums.add(expression.substring(i, j));
+                }
+                i = j;
+            }
+            j++;
+        }
+
+        String result = "0/1";
+        for (String frac : nums) {
+            result = add(result, frac);
+        }
+        return result;
+    }
+
+    private String add(String result, String frac) {
+        String[] frac1 = frac.split("/");
+        String[] frac2 = result.split("/");
+        int n1 = Integer.parseInt(frac1[0]);
+        int d1 = Integer.parseInt(frac1[1]);
+        int n2 = Integer.parseInt(frac2[0]);
+        int d2 = Integer.parseInt(frac2[1]);
+        int numerator = n1*d2 + n2*d1;
+        int denominator = d1*d2;
+        if (numerator == 0) return "0/1";
+
+        boolean negative = numerator*denominator < 0;
+        numerator = Math.abs(numerator);
+        denominator = Math.abs(denominator);
+        int gcd = getGCD(numerator, denominator);
+
+        return (negative ? "-" : "") + (numerator/gcd) + "/" + (denominator/gcd);
+    }
+
+    private int getGCD(int a, int b) {
+        if (a == 0 || b == 0) return a + b;
+        return getGCD(b, a%b);
+    }
+
+}
diff --git a/src/test/java/com/stevesun/_592Test.java b/src/test/java/com/stevesun/_592Test.java
@@ -0,0 +1,26 @@
+package com.stevesun;
+
+import com.stevesun.solutions._592;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+/**
+ * Created by stevesun on 5/23/17.
+ */
+public class _592Test {
+    private static _592 test;
+    private static String expression;
+
+    @BeforeClass
+    public static void setup(){
+        test = new _592();
+    }
+
+    @Test
+    public void test1(){
+        expression = "-1/2+1/2+1/3";
+        assertEquals("1/3", test.fractionAddition(expression));
+    }
+}
