Today is Saturday, I gonna review the tasks I've done this week, and finish today's leetcode's May LeetCoding Challenge with cpp.

LeetCode Review

Flatten Binary Tree to Linked List

too easy to review

Ambiguous Coordinates

too easy to review

Range Sum Query 2D - Immutable

too easy to review

Count Primes

too easy to review

Maximum Points You Can Obtain from Cards

class Solution {
public:
	int maxScore(vector<int>& cardPoints, int k) {
		int len = cardPoints.size();
		int sum = 0;
    for(int i = 0; i < k; ++i) {
      sum += cardPoints[i];
    }
    int answer = sum;
    for(int i = 0; i < k; ++i) {
      sum = sum - cardPoints[k - 1 - i] + cardPoints[len - 1 - i];
      answer = max(sum, answer);
    }
		return answer;
	}
};

May LeetCoding Challenge 15

Description

Valid Number

A valid number can be split up into these components (in order):

1. A decimal number or an integer.
2. (Optional) An 'e' or 'E', followed by an integer.

A decimal number can be split up into these components (in order):

1. (Optional) A sign character (either '+' or '-').
2. One of the following formats:
   1. At least one digit, followed by a dot '.'.
   2. At least one digit, followed by a dot '.', followed by at least one digit.
   3. A dot '.', followed by at least one digit.

An integer can be split up into these components (in order):

1. (Optional) A sign character (either '+' or '-').
2. At least one digit.

For example, all the following are valid numbers: ["2", "0089", "-0.1", "+3.14", "4.", "-.9", "2e10", "-90E3", "3e+7", "+6e-1", "53.5e93", "-123.456e789"], while the following are not valid numbers: ["abc", "1a", "1e", "e3", "99e2.5", "--6", "-+3", "95a54e53"].

Given a string s, return true if s is a valid number.

Example 1:

Input: s = "0"
Output: true

Example 2:

Input: s = "e"
Output: false

Example 3:

Input: s = "."
Output: false

Example 4:

Input: s = ".1"
Output: true

Constraints:

• 1 <= s.length <= 20
• s consists of only English letters (both uppercase and lowercase), digits (0-9), plus '+', minus '-', or dot '.'.

Solution

1A, haha

class Solution {
  int len;
  void checkSign(string &s, int &pos) {
    if(s[pos] == '+' || s[pos] == '-')
    pos += 1;
  }

  bool checkInteger(string &s, int &pos) {
    int initPos = pos;
    checkSign(s, pos);
    if(pos < len && isdigit(s[pos])) {
      while(pos < len && isdigit(s[pos])) pos += 1;
      return true;
    } else {
      pos = initPos;
      return false;
    }
  }

  bool checkDecimal(string &s, int &pos) {
    int initPos = pos;
    bool ok = true;
    checkSign(s, pos);
    bool hasFirst = false;
    if(pos < len && isdigit(s[pos])) {
      hasFirst = true;
      while(pos < len && isdigit(s[pos])) pos += 1;
    }
    if(pos < len && s[pos] == '.') {
      pos += 1;
    } else {
      pos = initPos;
      return false;
    }
    if(pos < len && isdigit(s[pos])) {
      while(pos < len && isdigit(s[pos])) pos += 1;
    } else if(!hasFirst) {
      pos = initPos;
      return false;
    }
    return true;
  }  
public:
  bool isNumber(string s) {
    int pos = 0;
    len = s.length();
    if(!(checkDecimal(s, pos) || checkInteger(s, pos))) {
      return false;
    }
    if(pos < len) {
      if(s[pos] != 'e' && s[pos] != 'E') return false;
      pos += 1;
      if(!checkInteger(s, pos)) {
        return false;
      }
    }
    return pos == len;
  }
};

or use regular expression

const regex re("^[-+]?((\\d+\\.\\d*)|(\\.\\d+)|\\d+)([eE][+-]?\\d+)?$");
class Solution {
public:
  bool isNumber(string s) {
    return regex_search(s, re);
  }
};