Questions and tests
package sword049;
/* 将一个字符串转换成一个整数，要求不能使用字符串转换整数的库函数。
* 数值为0或者字符串不是一个合法的数值则返回0
*/
public class main {
public static void main(String[] args) {
String [] testTable = {"123","+12","-569","+12345678901556","-2147483648","-2147483649","2147483647","2147483648","1a"};
for (String ito : testTable) {
test(ito);
}
}
private static void test(String ito) {
Solution solution = new Solution();
int rtn;
long begin = System.currentTimeMillis();
System.out.print(ito);
System.out.println();
//开始时打印数组
rtn= solution.strToInt(ito);//执行程序
long end = System.currentTimeMillis();
System.out.println("rtn=" );
System.out.print(rtn);
System.out.println();
System.out.println("耗时：" + (end - begin) + "ms");
System.out.println("-------------------");
}
}
Solution 1 (success)
Pay attention to the legality of the input data, such as "1234+12", "12@@#*24", these are all illegal values, and 0 should be returned. But if the first character is + or -, and it affects the last output symbol, it is necessary to judge whether the number is out of range at the end.
When calculating, first turn the number into a negative number. The range of int is [-2147483648,2147483647], and the smallest negative number can be calculated.
package sword049;
public class Solution {
public int strToInt(String s) {
int length = s.length();
int index = 0;
boolean isPositive = true;
if(s.charAt(index) == '+') {
index++;
}
if(s.charAt(index) == '-') {
index++;
isPositive = false;
}
int num = 0;
while(index<length) {
int now = s.charAt(index) - '0';
if(now < 0 || now > 9) {
return 0;
}
if(num < -214748364 ) {
return 0;
}
if(num == -214748364 ) {
if(isPositive) {
if(now > 7) {
return 0;
}
}else {
if(now > 8) {
return 0;
}
}
}
num = 10 * num - now;
index++;
}
if(isPositive) {
num = -num;
}
return num;
}
}