题解 | #累加出整个范围所有的数最少还需要几个数#

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main{
public static void main(String[] args) throws IOException {
BufferedReader sc = new BufferedReader(new InputStreamReader(System.in));
String str = sc.readLine();

    int result = process(str);

    System.out.println(result);

}

private static int process(String str) {
    if ("2147483648".equals(str) || !isValid(str)) {
        return 0;
    }

    if ("-2147483648".equals(str)) {
        return -2147483648;
    }

    int negetive = -1;
    if (str.charAt(0) == '-') {
        negetive = 1;
        str = str.substring(1);
    }

    if (!isValidDigit(str)){
        return 0;
    }

    char[] ch = str.toCharArray();
    int res = 0;

    int digit = 1;

    for (int i = ch.length - 1; i >= 0; i--) {
        int number = ch[i] - '0';
        res += number * digit;
        digit = digit * 10;
    }

    if (negetive == 1) {
        return -res;
    } else {
        return res;
    }

}

public static  boolean isValidDigit(String str){
    String temp = "2147483648";
    if (str.length()>temp.length()){
        return false;
    }
    else if(str.length()==temp.length()){
        char[] tempCh = temp.toCharArray();
        char[] strCh = str.toCharArray();
        for (int i = 0; i < strCh.length; i++) {
            if (strCh[i]>tempCh[i]){
                return false;
            }
        }
    }
    return true;
}


public static boolean isValid(String str) {
    char[] chars1 = str.toCharArray();
    if (chars1[0] != '-' && (chars1[0] < '0' || chars1[0] > '9')) {
        return false;
    }
    if (chars1[0] == '-' && (chars1.length == 1 || chars1[1] == '0')) {
        return false;
    }

    if (chars1[0] == '0' && chars1.length > 1) {
        return false;
    }

    for (int i = 1; i < chars1.length; i++) {
        if (chars1[i] < '0' || chars1[i] > '9') {
            return false;

        }
    }
    return true;
}

}