剑指Offer，把字符串转成整数

zebinh · zebinh · commit 01a274cd1dfd · 2019-12-19T21:27:41.000+08:00
diff --git a/swordoffer/StringToInt.java b/swordoffer/StringToInt.java
@@ -0,0 +1,48 @@
+/**
+ *  剑指Offer，把字符串转成整数
+ */
+
+public class StringToInt {
+
+    public static void main(String[] args) {
+        System.out.println(StrToInt("-2147483649"));
+    }
+
+    public static int StrToInt(String str) {
+        if (str == null || str.length() == 0) {
+            return 0;
+        }
+        if (str.charAt(0) != '+' && str.charAt(0) != '-'  && !(str.charAt(0) >= '0' && str.charAt(0) <= '9')) {
+            return 0;
+        }
+        for (int i = 1; i < str.length(); i++) {
+            if (! (str.charAt(i) >= '0' && str.charAt(i) <= '9') ) {
+                return 0;
+            }
+        }
+        int sum = 0;
+        int base = 1;
+        for (int i = str.length() - 1; i > 0; i--) {
+            sum += (str.charAt(i) - '0' ) * base;
+            base *= 10;
+        }
+        if (str.charAt(0) == '+') {
+             if (sum < 0) {
+                 sum = 0;
+             }
+        }else if(str.charAt(0) == '-') {
+            sum = 0-sum;
+            if (sum > 0) {
+                sum = 0;
+            }
+        }else{
+            sum += (str.charAt(0) - '0' ) * base;
+            if (sum < 0) {
+                sum = 0;
+            }
+        }
+        
+        return sum;
+    }
+    
+}
