#include <string>

class Solution {
  public:
    std::string minRemoveToMakeValid(std::string s) {
        int open = 0;

        for (auto i = 0u; i < s.size(); ++i) {
            switch (s[i]) {
            case '(':
                // opening
                ++open;
                break;
            case ')':
                if (open > 0) {
                    // can close
                    --open;
                } else {
                    // have to remove the closing paren
                    s.erase(i, 1);
                    --i;
                }
            }
        }

        // Remove the opening brackets from end
        for (auto i = s.size(); open > 0 && i-- > 0;) {
            if (s[i] == '(') {
                s.erase(i, 1);
                --open;
            }
        }

        return s;
    }
};

#ifdef _MF_TEST
#include <gtest/gtest.h>

namespace {
bool valid(const std::string &s) {
    int open = 0;

    for (char c : s) {
        switch (c) {
        case '(':
            ++open;
            break;
        case ')':
            if (open-- <= 0) {
                return false;
            }
            break;
        }
    }

    return open == 0;
}
} // namespace

TEST(valid, valid_strings) {
    EXPECT_TRUE(valid(""));
    EXPECT_TRUE(valid("(lee(t(c)o)de)"));
    EXPECT_TRUE(valid("lee(t(c)o)de"));
    EXPECT_TRUE(valid("(a)b(c)d"));
    EXPECT_TRUE(valid("ab(c)d"));
    EXPECT_TRUE(valid("(())(())"));
}

TEST(valid, invalid_strings) {
    EXPECT_FALSE(valid("lee(t(c)o)de)"));
    EXPECT_FALSE(valid("a)b(c)d"));
    EXPECT_FALSE(valid("))(("));
}

TEST(examples, _1) {
    Solution s;
    EXPECT_TRUE(valid(s.minRemoveToMakeValid("lee(t(c)o)de)")));
}

TEST(examples, _2) {
    Solution s;
    EXPECT_TRUE(valid(s.minRemoveToMakeValid("a)b(c)d")));
}

TEST(examples, _3) {
    Solution s;
    EXPECT_TRUE(valid(s.minRemoveToMakeValid("))((")));
}

int main(int argc, char **argv) {
    testing::InitGoogleTest(&argc, argv);
    return RUN_ALL_TESTS();
}
#endif