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Evaluate Reverse Polish Notation
Evaluate the value of an arithmetic expression in Reverse Polish Notation.
Valid operators are +
, -
, *
, /
. Each operand may be an integer or another expression.
Some examples:
["2", "1", "+", "3", "*"] -> ((2 + 1) * 3) -> 9 ["4", "13", "5", "/", "+"] -> (4 + (13 / 5)) -> 6
说明:使用一个数字栈即可。(也可用数组链表模拟栈)
inline int newPop(stack<int> &digits) { int v = digits.top(); digits.pop(); return v;}class Solution {public: int evalRPN(vector<string> &tokens) { stack<int> digits; for(size_t id = 0; id < tokens.size(); ++id) { if((tokens[id][0] == ‘-‘ && tokens[id].size() > 1 ) || (tokens[id][0] >= ‘0‘ && tokens[id][0] <= ‘9‘)) digits.push(atoi(tokens[id].c_str())); else { int v; switch(tokens[id][0]){ case ‘+‘: { digits.push(newPop(digits)+newPop(digits)); break; } case ‘-‘: { v = newPop(digits); digits.push(newPop(digits)-v); break; } case ‘*‘: { digits.push(newPop(digits)*newPop(digits)); break; } case ‘/‘: { v = newPop(digits); digits.push(newPop(digits)/v); break; } } } } return digits.top(); }};
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