A. 寒域爷的奇怪代码

int sum(int _Xx) {
	int ret = 0;
	for (int i = 1; i <= _Xx; i++) ret += i;
	return ret;
}

inline int sum(int _Xx) { return (1 + _Xx) * _Xx / 2; }

void bubble_sort(int* arr, int num) {
	for (int i = 0; i < num - 1; i++)
		for (int j = 0; j < num - i - 1; j++)
			if (arr[j] < arr[j + 1]) arr[j] ^= arr[j + 1] ^= arr[j] ^= arr[j + 1];
}

#include <queue>
void heap_sort(int* arr, int num) {
	std::priority_queue<int> heap;
	for (int i = 0; i < num; i++) heap.push(arr[i]);
	for (int i = 0; i < num; i++) {
		arr[i] = heap.top(); 
		heap.pop();
	}
}

long long int fibonacci(int _Xx) {
    if (_Xx <= 2) return 1;
    return fibonacci(_Xx - 1) + fibonacci(_Xx - 2);
}

#include <cstring>
long long int fibonacci(int _Xx) {
	static long long int save[1000];
	static bool first = true;
	if (first) first = false, memset(save, -1, sizeof(save));
	if (save[_Xx] != -1) return save[_Xx];
	if (_Xx <= 2) return 1;
	return save[_Xx] = fibonacci(_Xx - 1) + fibonacci(_Xx - 2);
}

#include <string>
int lengthOfLongestSubstring(std::string s) {
	int i, j, len = 0, maxx = 0;
	bool sign[30];
	memset(sign, 0, sizeof(sign));
	for (i = 0, j = 0; j < s.length(); ++j) {
		while (sign[s[j] - 'a'] == 1) {
			sign[s[i] - 'a'] = 0;
			++i;
		}
		sign[s[j] - 'a'] = 1;
		maxx = std::max(maxx, j - i + 1);
	}
	return maxx;
}