leetcode 栈和队列类型题

1，Valid Parentheses

 bool isVaild1(string& s) {  // 直接列举，不易扩展
     stack<char> stk;
     for (int i = ; i < s.length(); ++i) {
         if (stk.empty())
             stk.push(s[i]);
         else {
             char top = stk.top();
             if (top == '(' && s[i] == ')' || top == '{' && s[i] == '}' || top == '[' && s[i] == ']')
                 stk.pop();
         }
     }
     if (stk.empty())
         return true;
     else
         return false;
 }

 bool isValid2(string& s) {
     string left = "([{";
     string right = ")]}";
     stack<char> stk;

     for (auto c = s.begin(); c != s.end(); ++c) {
         if (left.find(*c) != string::npos)
             stk.push(*c);
         else {
             if (stk.empty() || stk.top() != left[right.find(*c)])
                 return false;
             else
                 stk.pop();
         }
     }
     return stk.empty();
 }

isVaild

2，Longest Valid Parentheses

 int longestValidParentheses(const string& s) {
     int len = ;
     stack<char> stk;

     for (size_t i = ; i < s.size(); ++i) {
         if (stk.empty())
             stk.push(s[i]);
         else {
             if (stk.top() == '(' && s[i] == ')') {
                 stk.pop();
                 ++len;
             }
             else
                 stk.push(s[i]);
         }
     }
     return  * len;
 }

longestValidParentheses

3，Largest Rectangle in Histogram

 int longestRectangleArea1(vector<int>& heights) {  // 暴力求解
     if (heights.size() == ) return ;
     int result = ;
     for (int i = ; i < heights.size(); ++i) {
         int minHeight = heights[i];
         if (i == heights.size() -  || heights[i]>heights[i + ]) {  // 简单优化
             for (int j = i; j >= ; --j) {
                 minHeight = min(minHeight,heights[j]);
                 result = max((i - j + )*minHeight, result);
             }
         }
     }
     return result;
 }

 int longestRectangleArea2(vector<int>& heights) {  // 用 stack实现，未看懂
     stack<int> s;
     heights.push_back();
     int result = ;
     for (int i = ; i < heights.size();) {
         if (s.empty() || heights[i] > heights[s.top()])
             s.push(i++);
         else {
             int temp = s.top();
             s.pop();
             result = max(result, heights[temp] * (s.empty() ? i : i - s.top() - ));
         }
     }
     return result;

 }

longestRectangleArea

4，Evaluate Reverse Polish Notation

 int evalRPN(vector<string>& tokens) {
     stack<int> stk;
     string options = "+-*/";
     for (int i = ; i < tokens.size(); ++i) {
         if (options.find(tokens[i]) == string::npos)  // 不是运算符
             stk.push(atoi(tokens[i].c_str()));
         else {
             int num1 = stk.top();
             stk.pop();
             int num2 = stk.top();
             stk.pop();

             if (tokens[i] == "+") stk.push(num1 + num2);
             else if (tokens[i] == "-") stk.push(num1 - num2);
             else if (tokens[i] == "*") stk.push(num1 * num2);
             else stk.push(num1 / num2);
         }
     }
     return stk.top();
 }

evalRPN

以上题目来源于：https://github.com/soulmachine/leetcode(leetcode-cpp.pdf)