147 lines
3.6 KiB
C++
147 lines
3.6 KiB
C++
#include <bits/stdc++.h>
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using namespace std;
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struct Node {
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char sign; // 运算符，叶子节点为 '?'
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long long num; // 数字
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Node* left;
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Node* right;
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Node(): sign('?'), num(-1), left(nullptr), right(nullptr) {}
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Node(char s): sign(s), num(-1), left(nullptr), right(nullptr) {}
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Node(long long n): sign('?'), num(n), left(nullptr), right(nullptr) {}
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};
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// 快速幂，整数
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long long fastpow(long long base, long long exp){
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long long res = 1;
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while(exp > 0){
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if(exp & 1) res *= base;
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base *= base;
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exp >>= 1;
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}
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return res;
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}
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// 运算优先级
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int level(char c){
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switch(c){
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case '+': case '-': return 1;
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case '*': case '/': return 2;
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case '^': return 3;
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default: return 0;
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}
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}
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// 找到最外层优先级最低的运算符
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int findexp(const string &s, int l, int r){
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int pos = -1;
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int minLevel = 114514;
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int balance = 0; // 括号深度
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for(int i = r; i >= l; --i){ // 右结合，优先找右边
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if(s[i] == ')') balance++;
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else if(s[i] == '(') balance--;
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else if(balance == 0 && level(s[i]) > 0){
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if(level(s[i]) <= minLevel){
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minLevel = level(s[i]);
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pos = i;
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}
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}
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}
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return pos;
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}
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// 字符串转整数
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long long toNum(const string &s, int l, int r){
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long long tmp = 0;
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while(l <= r && isspace((unsigned char)s[l])) l++;
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while(r >= l && isspace((unsigned char)s[r])) r--;
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if(l > r) return 0;
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for(int i = l; i <= r; ++i){
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if(!isdigit(s[i])) return 0;
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tmp = tmp * 10 + (s[i] - '0');
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}
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return tmp;
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}
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class Expression {
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public:
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string exp;
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Node* root;
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long long result;
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bool isValid;
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Expression(const string &s): exp(s), root(nullptr), result(0), isValid(true) {}
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Node* build(const string &s, int l, int r){
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while(l <= r && s[l] == ' ') l++;
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while(l <= r && s[r] == ' ') r--;
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if(l > r) return nullptr;
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// 外层括号处理
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if(s[l] == '(' && s[r] == ')'){
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int balance = 0;
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bool hasOuter = true;
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for(int i = l; i <= r; ++i){
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if(s[i] == '(') balance++;
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else if(s[i] == ')') balance--;
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if(balance == 0 && i < r){
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hasOuter = false;
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break;
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}
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}
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if(hasOuter) return build(s, l+1, r-1);
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}
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int pos = findexp(s, l, r);
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if(pos == -1){
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long long val = toNum(s, l, r);
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return new Node(val);
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}
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Node* tmp = new Node(s[pos]);
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tmp->left = build(s, l, pos-1);
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tmp->right = build(s, pos+1, r);
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return tmp;
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}
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long long calc(Node* r, bool &v){
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if(!r) return 0;
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if(r->sign == '?') return r->num;
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long long left = calc(r->left, v);
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long long right = calc(r->right, v);
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switch(r->sign){
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case '+': return left + right;
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case '-': return left - right;
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case '*': return left * right;
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case '/':
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if(right == 0){ v = false; return 0; }
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return left / right;
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case '^':
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if(right < 0){ v = false; return 0; }
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return fastpow(left, right);
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default: return 0;
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}
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}
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void calc(){
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isValid = true;
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result = calc(root, isValid);
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}
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};
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int main(){
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string s;
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while(getline(cin, s)){
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Expression tree(s);
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tree.root = tree.build(s, 0, s.length()-1);
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tree.calc();
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if(tree.isValid) cout << tree.result << endl;
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else cout << "INVALID" << endl;
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}
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return 0;
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}
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