private static int pivotPartition(int A[], int bt, int ed) {
		// 取中间值作为stand，防止数组有序出现O(n^2)情况
		swapVar(A, bt, ed);

		int stand = A[bt];

		while (bt < ed) {
			while (bt < ed && A[ed] >= stand) {
				ed--;
			}
			if (bt < ed) {
				A[bt++] = A[ed];
			}

			while (bt < ed && A[bt] <= stand) {
				bt++;
			}
			if (bt < ed) {
				A[ed--] = A[bt];
			}
		}

		A[bt] = stand;

		return bt;
	}