C++ compilation error: Too deep recursion causes stack overflow. How to solve it?

C is a widely used programming language, and it is inevitable to encounter various errors during its compilation and execution. One common mistake is to recurse too deep and cause a stack overflow.

In recursion, when there are too many recursion levels, the program will encounter stack overflow errors. This is because recursive functions require a certain amount of memory space to store local variables and function calls during each recursion. Each recursion will push these local variables and function calls into the function call stack. The size of the stack is limited. Once this limit is exceeded, a stack overflow will occur, causing the program to crash.

So, how should we solve the stack overflow caused by too deep recursion? Here are several solutions.

1. Rewrite recursion as loop

The essence of recursive function is a loop with backtracking, so without affecting the program logic, we can rewrite the recursive function as cycle. This can reduce the overhead caused by recursion, thereby reducing the risk of stack overflow.

For example, the following is a recursive function that calculates the Fibonacci sequence:

int fib(int n) {
    if (n == 0 || n == 1) {
        return n;
    }
    return fib(n - 1) + fib(n - 2);
}

We can rewrite it in the following loop form:

int fib(int n) {
    if (n == 0 || n == 1) {
        return n;
    }
    int a = 0, b = 1;
    for (int i = 2; i <= n; i++) {
        int c = a + b;
        a = b;
        b = c;
    }
    return b;
}

2. Increase the stack Space

We can avoid stack overflow by setting the size of the stack space. Under Windows, this can be achieved by modifying the stack space size of the program's executable file; under Linux, you can use the ulimit command to control the stack size. One thing to note with this approach is that too much stack space will occupy system resources, so you need to weigh the pros and cons.

3. Adjust the recursive algorithm

Sometimes, the recursive algorithm itself may have problems, resulting in too many recursive levels. In this case, we need to optimize the recursive algorithm and reduce the number of recursive calls to reduce the risk of stack overflow.

For example, the following is a recursive algorithm for solving the Fibonacci sequence:

int fib(int n) {
    if (n == 0 || n == 1) {
        return n;
    }
    return fib(n - 1) + fib(n - 2);
}

We can optimize this algorithm through memoized search to reduce the number of recursive calls:

int fib(int n, unordered_map<int, int>& memo) {
    if (n == 0 || n == 1) {
        return n;
    }
    if (memo.find(n) != memo.end()) {
        return memo[n];
    }
    int ans = fib(n - 1, memo) + fib(n - 2, memo);
    memo[n] = ans;
    return ans;
}

int fib(int n) {
    unordered_map<int, int> memo;
    return fib(n, memo);
}

4. Avoid repeated calculations of recursive functions

In recursive functions, there may be sub-problems of repeated calculations. We can avoid this using a caching mechanism to reduce the number of recursive calls.

For example, if we need to calculate a Catalan number, we can use the caching mechanism to avoid repeated calculations:

int catalan(int n, unordered_map<int, int>& memo) {
    if (n <= 1) {
        return 1;
    }
    if (memo.find(n) != memo.end()) {
        return memo[n];
    }
    int ans = 0;
    for (int i = 0; i < n; i++) {
        ans += catalan(i, memo) * catalan(n - 1 - i, memo);
    }
    memo[n] = ans;
    return ans;
}

int catalan(int n) {
    unordered_map<int, int> memo;
    return catalan(n, memo);
}

In short, there are many ways to avoid stack overflow caused by too deep recursion. We need to use Choose the appropriate method for the specific situation. When writing recursive functions, be sure to pay attention to the depth of recursion and fully test to ensure that the program runs correctly.

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