189. Rotate Array

189. Rotate Array

Rotate an array of (n) elements to the right by (k) steps.

For example, with (n = 7) and (k = 3), the array [1,2,3,4,5,6,7] is rotated to [5,6,7,1,2,3,4].

Related problem: Reverse Words in a String II

限制为 (O(1)) extra space 的话, 相对有难度.
人家很帅屁的方法:
[1,2,3,4,5,6,7] Original
[7,6,5,4,3,2,1] A[0..n-1] reverse
[5,6,7,4,3,2,1] A[0..k-1] reverse
[5,6,7,1,2,3,4] A[k..n-1] reverse

按人家思路,自己写的代码:

void rotate(vector<int>& A, int k) {
    int n = A.size();
    k %= n;
    if (n == 0 || n == 1 || k >= n) return;
    reverse(A, 0, n - 1);
    reverse(A, 0, k - 1);
    reverse(A, k, n - 1);
}

void reverse(vector<int>& A, int start, int end) {
    int temp;
    //代码简洁明了
    while (start < end) { //注意条件
        temp = A[start];
        A[start] = A[end];
        A[end] = temp;
        start++;
        end--;
    }
    // start and end are the index based on 0
    // 自己写的这个有些复杂并且还错了!!!
    // int temp, n = end - start + 1;
    // for (int i = start; i <= (n-1)/2; i++){
    //     temp = A[i];
    //     A[i] = A[n - (i + 1)];
    //     A[n - (i + 1)] = temp;
    // }
}