前缀和和状态码：
class Solution {
public:int findTheLongestSubstring(string s) {
int ans = 0, status = 0, n = s.size();vector<int> pos(32, -1);pos[0] = 0;for (int i = 0; i < n; i ++) {
if (s[i] == 'a') {
status ^= 1<<0;} else if (s[i] == 'e') {
status ^= 1<<1;} else if (s[i] == 'i') {
status ^= 1<<2;} else if (s[i] == 'o') {
status ^= 1<<3;} else if (s[i] == 'u') {
status ^= 1<<4;}if (pos[status] != -1) {
ans = max(ans, i + 1 - pos[status]);} else {
pos[status] = i + 1;}}return ans;}
};