# 表达式的值

``````给一个用字符串表示的表达式数组，求出这个表达式的值。

``````static bool cmp[][7] =
{
{0,0,0,0,0,0,0},
{1,1,1,0,0,0,1},
{1,1,1,0,0,0,1},
{1,1,1,1,1,0,1},
{1,1,1,1,1,0,1},
{1,0,0,0,0,0,1},
{1,0,0,0,0,0,0}
};

static const vector<string> operators = {"#", "+", "-", "*", "/", "(", ")"};

int evaluateExpression(vector<string> &expression) {

static unordered_map<string, int> hash;

for (int i = 0; i < operators.size(); ++i) {
hash[operators[i]] = i;
}

vector<int> optr(1, 0); // expression extended to  "#" expression "#"

vector<double> oprd;

expression.push_back("#");``````
``````    for (auto e : expression) {
auto iter = hash.find(e);
if (iter == hash.end()) {
oprd.push_back(atoi(e.c_str()));
continue;
}
int idx = iter->second;
while (true) {
int prior = optr.back();

if (!cmp[prior][idx]) {
optr.push_back(idx);
break;
}

optr.pop_back();

if (prior == 5) { break; }

double b = oprd.back();
oprd.pop_back();

double a = oprd.back();
oprd.pop_back();

switch (prior) {
case 1 :
oprd.push_back(a + b);
break;
case 2 :
oprd.push_back(a - b);
break;
case 3 :
oprd.push_back(a * b);
break;
case 4 :
oprd.push_back(a / b);
break;
}
}
}
return oprd.empty() ? 0 : static_cast<int>(oprd.back());
}
``````

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