【C++刷题】优选算法——栈

最新推荐文章于 2025-06-12 23:09:27 发布

原创最新推荐文章于 2025-06-12 23:09:27 发布

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#c++ #算法 #开发语言

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删除字符串中的所有相邻重复项

string removeDuplicates(string s) {
    string ret;
    for (char c : s) {
        if (ret.empty() || c != ret.back()) {
            ret += c;
        } else {
            ret.pop_back();
        }
    }
    return ret;
}

比较含退格的字符串

bool backspaceCompare(string s, string t) {
    string stack_s, stack_t;
    for (char c : s) {
        if (c == '#') {
            if (!stack_s.empty()) {
                stack_s.pop_back();
            }
        } else {
            stack_s += c;
        }
    }
    for (char c : t) {
        if (c == '#') {
            if (!stack_t.empty()) {
                stack_t.pop_back();
            }
        } else {
            stack_t += c;
        }
    }
    return stack_s == stack_t;
}

基本计算器 II

int calculate(string s) {
    vector<int> v;
    char op = '+';
    int i = 0;
    while (i < s.size()) {
        switch (s[i]) {
        case '+':
            op = '+';
            ++i;
            break;
        case '-':                
            op = '-';
            ++i;
            break;
        case '*':
            op = '*';
            ++i;
            break;
        case '/':
            op = '/';
            ++i;
            break;
        case ' ':
            ++i;
            break;
        default:
            int tmp = 0;
            while (i < s.size() && s[i] >= '0' && s[i] <= '9') {
                tmp = tmp * 10 + (s[i] - '0');
                ++i;
            }
            switch (op) {
                case '+':
                    v.push_back(tmp);
                    break;
                case '-':
                    v.push_back(-tmp);
                    break;
                case '*':
                    v.back() *= tmp;
                    break;
                case '/':
                    v.back() /= tmp;
                    break;
                } // end switch(op)
            break;
        } // end switch(s[i])
    } // while (i < s.size())
    int ret = 0;
    for (int i = 0; i < v.size(); ++i) {
        ret += v[i];
    }
    return ret;
}

字符串解码

string decodeString(string s) {
    vector<int> stack_num;
    vector<string> stack_str(1);

    int i = 0;
    while (i < s.size()) {
        if (s[i] >= '0' && s[i] <= '9') {
            stack_num.push_back(0);
            while (i < s.size() && s[i] >= '0' && s[i] <= '9') {
                stack_num.back() = stack_num.back() * 10 + (s[i] - '0');
                ++i;
            }
        }
        else if (s[i] == '[') {
            ++i;
            stack_str.push_back("");
            while (i < s.size() && s[i] >= 'a' && s[i] <= 'z') {
                stack_str.back() += s[i];
                ++i;
            }
        }
        else if (s[i] == ']') {
            while (stack_num.back()--) {
                stack_str[stack_str.size() - 1 - 1] += stack_str.back();
            }
            stack_num.pop_back();
            stack_str.pop_back();
            ++i;
        }
        else {
            while (i < s.size() && s[i] >= 'a' && s[i] <= 'z') {
                stack_str.back() += s[i];
                ++i;
            }
        }
    }
    return stack_str.back();
}

验证栈序列

bool validateStackSequences(vector<int>& pushed, vector<int>& popped) {
    stack<int> push;
    int i = 0;
    for (int e : pushed) {
        if (e == popped[i]) {
            ++i;
            while (!push.empty() && push.top() == popped[i]) {
                push.pop();
                ++i;
            }
        }
        else push.push(e);
    }
    return i == popped.size();
}