元素查找

public int findElement(int[] A, int n, int x) {
//return findElementHelp(A, 0, n - 1, x);
if (n == 1) {
return 0;
} else {
if (n == 2) {
if (A[0] == x) {
return 0;
} else {
return 1;
}
}
}
if (A[0] < A[n - 1]) {
return Arrays.binarySearch(A, 0, n, x);
}
int left = 0;
int right = n;

if (A[0] < A[1]) {//先升后升，（注意不是先升后降）
while (left < right) {
int mid = (left + right) / 2;
if (mid != 0 && mid != (n - 1) && A[mid] > A[mid + 1] && A[mid - 1] < A[mid]) {//如果找到拐点
return Math.max(Arrays.binarySearch(A, 0, mid + 1, x), Arrays.binarySearch(A, mid + 1, n, x));
} else {
if (A[mid] > A[0]) {
left = mid + 1;
} else {
right = mid;
}
}
}
} else {
while (left < right) {
int mid = (left + right) / 2;
if (mid != 0 && mid != (n - 1) && A[mid] < A[mid + 1] && A[mid - 1] > A[mid]) {//如果找到拐点
return Math.max(
downBinarySearch(A, 0, mid + 1, x),
Arrays.binarySearch(A, mid + 1, n, x));
} else {
if (A[mid] > A[n - 1]) {
left = mid + 1;
} else {
right = mid;
}
}
}
}
return -1;
}

private int downBinarySearch(int[] A, int left, int right, int x) {

while (left < right) {
int mid = (left + right) / 2;
if (A[mid] == x) {
return mid;
} else {
if (A[mid] < x) {
right = mid;
} else {
left = mid + 1;
}
}
}
return -1;
}