完成String转换int的函数。

shengshijun · shengshijun · commit 073f4e5b8719 · 2015-02-27T17:58:14.000+08:00
diff --git a/src/main/java/ssj/algorithm/math/MathUtil.java b/src/main/java/ssj/algorithm/math/MathUtil.java
@@ -219,6 +219,35 @@ public static int uglyNumber(int index) {
         return ugly_numbers[index - 1];
     }
 
+    public static int strToInt(String str) {
+        Preconditions.checkNotNull(str);
+        Preconditions.checkArgument(str.length() > 0);
+        Preconditions.checkArgument(!(str.length() == 1 && (str.charAt(0) == '+' || str.charAt(0) == '-')));
+        int result = 0;
+        boolean is_negative = false;
+        int num_start = 0;
+        if (str.charAt(0) == '-') {
+            is_negative = true;
+            num_start = 1;
+        } else if (str.charAt(0) == '+') {
+            num_start = 1;
+        }
+
+        for (int i = num_start; i < str.length(); i++) {
+            int this_digit = str.charAt(i) - '0';
+            if (this_digit < 0 || this_digit > 9) {
+                throw new ArithmeticException("wrong format");
+            }
+            result = Math.multiplyExact(result, 10);
+            if (is_negative) {
+                result = Math.subtractExact(result, this_digit);
+            } else {
+                result = Math.addExact(result, this_digit);
+            }
+        }
+        return result;
+    }
+
     public int closestBig(int origion) {
         Preconditions.checkArgument(origion > 0);
         int first_one_index = BitUtil.firstBitOne(origion);
diff --git a/src/main/java/ssj/algorithm/string/StringUntil.java b/src/main/java/ssj/algorithm/string/StringUntil.java
@@ -67,6 +67,7 @@ public static boolean uniqueChar(String s) {
 
     /**
      * 判断是不是变位词。
+     *
      * @param s1
      * @param s2
      * @return
@@ -174,6 +175,7 @@ public int search(String str) {
      * 假设字符串平均长度m，字符串个数n。
      * 第一步复杂度是O(nmlgm)，第二步复杂度是O(n)
      * 所以算法总体的复杂度就是O(nmlgm)
+     *
      * @param words
      * @return
      */
diff --git a/src/test/java/ssj/algorithm/Main.java b/src/test/java/ssj/algorithm/Main.java
@@ -1,13 +1,12 @@
 package ssj.algorithm;
 
-import ssj.algorithm.math.MathUtil;
-
 /**
  * Created by shenshijun on 15/2/1.
  */
 public class Main {
 
     public static void main(String[] args) {
-        System.out.println(MathUtil.uglyNumber(1500));
+        System.out.println(Integer.MAX_VALUE + 2L);
+//        int i = 2147483648;
     }
 }
diff --git a/src/test/java/ssj/algorithm/math/MathUtilTest.java b/src/test/java/ssj/algorithm/math/MathUtilTest.java
@@ -3,8 +3,7 @@
 import org.junit.Test;
 import ssj.algorithm.lang.Tuple2;
 
-import static org.junit.Assert.assertArrayEquals;
-import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.*;
 
 /**
  * Created by shenshijun on 15/2/26.
@@ -29,4 +28,53 @@ public void testCountNumberOne() {
     public void testCombineMinNumber() {
         assertArrayEquals(new Integer[]{321, 32, 3}, MathUtil.combineMinNumber(new Integer[]{3, 32, 321}));
     }
+
+    @Test
+    public void testStrToInt() {
+        assertEquals(10000, MathUtil.strToInt("10000"));
+        assertEquals(-10000, MathUtil.strToInt("-10000"));
+        assertEquals(0, MathUtil.strToInt("-0"));
+        assertEquals(0, MathUtil.strToInt("+0"));
+        assertEquals(Integer.MAX_VALUE, MathUtil.strToInt(String.valueOf(Integer.MAX_VALUE)));
+        assertEquals(Integer.MIN_VALUE, MathUtil.strToInt(String.valueOf(Integer.MIN_VALUE)));
+        try {
+            MathUtil.strToInt("+");
+            fail("never go here");
+        } catch (Exception e) {
+        }
+
+        try {
+            MathUtil.strToInt("-");
+            fail("never go here");
+        } catch (Exception e) {
+
+        }
+
+        try {
+            MathUtil.strToInt("");
+            fail("never go here");
+        } catch (Exception e) {
+        }
+
+        try {
+            MathUtil.strToInt("-10292a292983");
+            fail("never go here");
+        } catch (Exception e) {
+
+        }
+
+        try {
+            MathUtil.strToInt(String.valueOf(Integer.MAX_VALUE + 10L));
+            fail("never go here");
+        } catch (Exception e) {
+
+        }
+
+        try {
+            MathUtil.strToInt(String.valueOf(Integer.MIN_VALUE - 10L));
+            fail("never go here");
+        } catch (Exception e) {
+
+        }
+    }
 }

Original file line number	Diff line number	Diff line change
`@@ -1,13 +1,12 @@`
`1`	`1`	`package ssj.algorithm;`
`2`	`2`
`3`		`-import ssj.algorithm.math.MathUtil;`
`4`		`-`
`5`	`3`	`/**`
`6`	`4`	`* Created by shenshijun on 15/2/1.`
`7`	`5`	`*/`
`8`	`6`	`public class Main {`
`9`	`7`
`10`	`8`	`public static void main(String[] args) {`
`11`		`- System.out.println(MathUtil.uglyNumber(1500));`
	`9`	`+ System.out.println(Integer.MAX_VALUE + 2L);`
	`10`	`+// int i = 2147483648;`
`12`	`11`	`}`
`13`	`12`	`}`