code4offer-13 把字符串转换成整数

Unsolved

问题描述

分析

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public int StrToInt(String str) {
    int len = str.length();
    if (len == 0) return 0;
    int numLength = len;
    int sign = 1;
    if (str.charAt(0) == '-' || str.charAt(0) == '+') --numLength;
    if (str.charAt(0) == '-') {
        sign = -1;
    }

    long result = 0;
    int carry = 1;

    for(int i = len - 1; i >= len - numLength; --i) {
        if (str.charAt(i) >= '0' && str.charAt(i) <= '9') {
            if (sign > 0 && result > Integer.MAX_VALUE - (str.charAt(i)-'0') * carry) {
                return 0;
            }else if (sign < 0 && -result < Integer.MIN_VALUE + (str.charAt(i)-'0') * carry) {
                return 0;
            }
            result += (str.charAt(i)-'0') * carry;
            carry *= 10;
        } else {
            return 0;
        }
    }
    return (int)result * sign;
}