Example 1:
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Input: n = 1
Output: "foobar"
Explanation: There are two threads being fired asynchronously. One of them calls foo(), while the other calls bar(). "foobar" is being output 1 time.
Example 2:
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Input: n = 2
Output: "foobarfoobar"
Explanation: "foobar" is being output 2 times.

class FooBar {
private:
    int n;
    pthread_mutex_t t1=PTHREAD_MUTEX_INITIALIZER;
    pthread_mutex_t t2=PTHREAD_MUTEX_INITIALIZER;
public:
    FooBar(int n) {
        this->n = n;
        pthread_mutex_lock(&t1);
​
​
    }
​
    void foo(function<void()> printFoo) {
​
        for (int i = 0; i < n; i++) {
            pthread_mutex_lock(&t2);
​
            // printFoo() outputs "foo". Do not change or remove this line.
            printFoo();
            pthread_mutex_unlock(&t1);
        }
    }
​
    void bar(function<void()> printBar) {
        for (int i = 0; i < n; i++) {
            pthread_mutex_lock(&t1);
​
            // printBar() outputs "bar". Do not change or remove this line.
            printBar();
            pthread_mutex_unlock(&t2);
​
        }
    }
};