NumberOfDiscIntersections

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problem

solution

經典stack 教材

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// you can use includes, for example:
// #include <algorithm>

// you can write to stdout for debugging purposes, e.g.
// cout << "this is a debug message" << endl;

#include<stack>
int solution(string &S) {
    // write your code in C++14 (g++ 6.2.0)
    stack<char> sta;
    for(char c:S){
        if(c=='(' || c=='[' || c=='{') sta.push(c);
        else{
            if(sta.empty()) return false;
            else if(sta.top() == '(' && c==')') sta.pop();
            else if(sta.top() == '[' && c==']') sta.pop();
            else if(sta.top() == '{' && c=='}') sta.pop();
            else return false;
        }
    }
    return sta.empty();
}

analysis

  • time complexity O(n)
  • space complexity O(n)