8. String to Integer (atoi)

 

https://leetcode.com/problems/string-to-integer-atoi/discuss/4672/JAVA-Easy-Version-To-Understand!!!!!!!!!!

用sum = sum*10 + 这位数字来计算

不能直接通过-Integer.MIN_VALUE来取负

 

 1 class Solution {
 2     public int myAtoi(String str) {
 3         str = str.trim();
 4         if(str.length() == 0) return 0;
 5         long sum = 0;
 6         int sign = 1, start = 0;
 7         if(str.charAt(0) == '-'){
 8             sign = -1;
 9             start++;
10         }else if(str.charAt(0) == '+'){
11             start++;
12         }
13         for(int i = start; i < str.length(); i++){
14             if(Character.isDigit(str.charAt(i))){
15                 sum = sum*10 + (str.charAt(i) - '0');
16                 if(sign == 1 && sum > Integer.MAX_VALUE){
17                     return Integer.MAX_VALUE;
18                 }else if(sign == -1 && sum*sign < Integer.MIN_VALUE){
19                     return Integer.MIN_VALUE;
20                 }
21             }else{
22                 break;
23             }
24         }
25         return (int)sum * sign;
26         
27     }
28 }

 

 

 

 

 

 

 

 

 1 class Solution {
 2     public int myAtoi(String str) {
 3         str = str.trim();
 4         if(str.length() == 0) return 0;
 5         long res = 0;
 6         StringBuilder sb = new StringBuilder();
 7         if(str.charAt(0) == '+' || str.charAt(0) == '-' || (((str.charAt(0) - '0') >= 0) &&((str.charAt(0) - '0') <= 9))){
 8             if(((str.charAt(0) - '0') > 0) &&((str.charAt(0) - '0') <= 9)){
 9                 sb.append(str.charAt(0));
10             }
11             for(int i = 1; i < str.length(); i++){
12                 if(((str.charAt(i) - '0') >= 0) &&((str.charAt(i) - '0') <= 9)){
13                     if(str.charAt(i) == '0' && sb.length() == 0){ //开头是0不加入
14                         continue;
15                     }
16                     sb.append(str.charAt(i));
17                 }else{
18                     break;
19                 }
20                 
21             }
22             if(sb.length() == 0) return 0;  //没有得到数字
23             if(sb.length() > 10){     //超过10位就是超过int的边界 直接可以return
24                 if(str.charAt(0) == '-'){
25                     return Integer.MIN_VALUE;
26                 }else{
27                     return Integer.MAX_VALUE;
28                 }
29             }
30             res = Long.parseLong(sb.toString());
31             if(str.charAt(0) == '-'){
32                 res = -res;
33                 return (res < Integer.MIN_VALUE) ? Integer.MIN_VALUE : (int)res;
34                 
35             }
36             return (res > Integer.MAX_VALUE) ? Integer.MAX_VALUE : (int)res;
37             
38             
39         }else{
40             return (int)res;
41         }
42         
43     }
44 }

 

posted @ 2018-10-08 03:37  jasoncool1  阅读(79)  评论(0)  编辑  收藏  举报