LeetCode: Valid Number http://oj.leetcode.com/problems/valid-number/

valid_number.cpp

/**
 * determines whether a string is numeric
 * LeetCode: http://oj.leetcode.com/problems/valid-number/
 */

class Solution {
public:
    bool isSign(const char c) {
        return c == '-' || c == '+';
    }
    
    bool isInt(const char *s, int l, int h, bool sign=true) {
        if (sign && isSign(s[l])) l++;
        if (l > h)
            return false;
            
        for (int i = l; i <= h; i++) {
            if (!isdigit(s[i]))
                return false;
        }
        return true;
    }
    
    bool isFloat(const char *s, int l, int h, bool sign=true) {
        if (sign && isSign(s[l])) l++;
        int idx = -1;
        for (int i = l; i <= h; i++) {
            if (s[i] == '.') {
                idx = i;
                break;
            }
        }
        
        if (idx >= 0) {
            int hm = idx - 1;
            int lm = idx + 1;
            if (l > hm)
                return isInt(s, lm, h, false);  // .123
            else if (lm > h)
                return isInt(s, l, hm);  // 12.
            else
                return isInt(s, l, hm) && isInt(s, lm, h, false);  //12.23
        }
    }
    
    bool isHex(const char *s, int l, int h) {
        if (isSign(s[l])) l++;
        int len = h - l + 1;
        if (len>2 && s[l] == '0' && (s[l+1] == 'x' || s[l+1] == 'X')) {
            for (int i = l + 2; i <= h; i++) {
                if (!isxdigit(s[i]))
                    return false;
            }
            return true;
        }
        else
            return false;
    }
    
    bool isSci(const char *s, int l, int h) {
        if (isSign(s[l])) l++;
        int idx = -1;
        for (int i = l; i <= h; i++) {
            if (s[i] == 'e' || s[i] == 'E') {
                idx = i;
                break;
            }
        }
        
        if (idx >= 0) {
            int hm = idx - 1;
            int lm = idx + 1;
            
            return (isFloat(s, l, hm) || isInt(s, l, hm)) && isInt(s, lm, h);
        }
        else
            return false;
    }
    
    bool isNumber(const char *s, int l, int h) {
        return isInt(s, l, h) || isFloat(s, l, h) ||
               isHex(s, l, h) || isSci(s, l, h);
    }
    
    bool isNumber(const char *s) {
        // Note: The Solution object is instantiated only once and is reused by each test case.
        int l = 0, h = strlen(s) - 1;
        
        // remove spaces
        while (s[l] == ' ') l++;
        while (s[h] == ' ') h--;
        return isNumber(s, l, h);
    }
};