Poison

65. Valid Number

发表于 
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class Solution {
    public boolean isNumber(String s) {
        boolean hasDot = false, hasNumber = false;

        // 注意符号位仅能出现在开头
        for (int i = getNumStartIndex(s, 0); i < s.length(); i++) {
            char c = s.charAt(i);
            if (c == 'e' || c == 'E') {
                if (!hasNumber) {
                    return false;
                }

                return isInt(s, i + 1);
            } else if (c >= '0' && c <= '9') {
                hasNumber = true;
            } else if (c == '.') {
                if (!hasDot) {
                    hasDot = true;
                } else {
                    return false;
                }
            } else {
                return false;
            }
        }

        return hasNumber;
    }

    private int getNumStartIndex(String s, int i) {
        if (i == s.length()) {
            return i;
        }

        char c = s.charAt(i);
        return c == '+' || c == '-' ? i + 1 : i;
    }

    private boolean isInt(String s, int i) {
        i = getNumStartIndex(s, i);
        if (i == s.length()) {
            return false;
        }

        while (i < s.length()) {
            char c = s.charAt(i);
            if (c < '0' || c > '9') {
                return false;
            }
            i++;
        }

        return true;
    }
}
Reference

65. Valid Number