2021-12-25 Daily-Challenge

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In: DailyChallenge

Today I have done leetcode's December LeetCoding Challenge with cpp.

December LeetCoding Challenge 25

Description

Basic Calculator II

Given a string s which represents an expression, evaluate this expression and return its value.

The integer division should truncate toward zero.

You may assume that the given expression is always valid. All intermediate results will be in the range of [-231, 231 - 1].

Note: You are not allowed to use any built-in function which evaluates strings as mathematical expressions, such as eval().

Example 1:

Input: s = "3+2*2"
Output: 7

Example 2:

Input: s = " 3/2 "
Output: 1

Example 3:

Input: s = " 3+5 / 2 "
Output: 5

Constraints:

  • 1 <= s.length <= 3 * 105
  • s consists of integers and operators ('+', '-', '*', '/') separated by some number of spaces.
  • s represents a valid expression.
  • All the integers in the expression are non-negative integers in the range [0, 231 - 1].
  • The answer is guaranteed to fit in a 32-bit integer.

Solution

auto speedup = [](){
  cin.tie(nullptr);
  cout.tie(nullptr);
  ios::sync_with_stdio(false);
  return 0;
}();
class Solution {
public:
  int calculate(string s) {
    s.push_back('+');
    char prevSign = '+';
    int prev = 0;
    int cur = 0;
    int result = 0;
    for(auto c : s) {
      if(c == ' ') continue;
      if(isdigit(c)) {
        cur *= 10;
        cur += c - '0';
        continue;
      }
      if(prevSign == '+' || prevSign == '-') {
        result += prev;
        prev = prevSign == '+' ? cur : -cur;
      } else if(prevSign == '*') {
        prev = prev * cur;
      } else {
        prev = prev / cur;
      }
      prevSign = c;
      cur = 0;
    }
    return result + prev;
  }
};

// Accepted
// 109/109 cases passed (4 ms)
// Your runtime beats 98.87 % of cpp submissions
// Your memory usage beats 75.38 % of cpp submissions (7.9 MB)
Algorithm