旋转数组之元素查找

转载请注明作者与出处： franciscolv http://www.cnblogs.com/franciscolv/archive/2011/11/21/2257536.html

折半算法的改进 O(lgn)

    /**
     * 折半
     * @param a
     * @param k
     * @return
     */
    public static int findK0(int[] a, int k) {
        if (a == null)
            return -1;
        int l = 0, r = a.length;
        while (l + 1 < r) {
            int m = l + (r - l) / 2;
            if (a[m] >= a[l]) {
                if (k < a[m]) {
                    if (k >= a[l])
                        r = m;
                    else
                        l = m;
                } else {
                    l = m;
                }
            } else {
                if (k >= a[m]) {
                    if (k <= a[r - 1])
                        l = m;
                    else
                        r = m;
                } else {
                    r = m;
                }
            }
        }
        return a[l] == k ? l : -1;
    }