reverse反转数组

vector v = {1,2,3,4};
reverse(v.begin(), v.end());
// v 变成 {4,3,2,1}

int a[] = {1,2,3,4};
int n = 4;
reverse(a, a + n);
// a 变成 {4,3,2,1}

string s = “1234”;
reverse(s.begin(), s.end());
// s 变成 “4321”