求数组中第三大的数字，如果不存在则返回最大的数字

要求：算法时间复杂度为O(n)。

代码：

public int getThirdMaxElement(int[] array) {
		if(array == null) {
			return 0;
		}
		if(array.length == 1) {
			return array[0];
		}
		if(array.length == 2) {
			return array[0] > array[1] ? array[0] : array[1];
		}

		int[] thirdArr = {0,0,0}; //数组存储最大的三个数
		int a = 0;  //thirdArr数组下标
		int b = 1;	//array数组下标

		thirdArr[0] = array[0];
		//填充thirdArr数组
		while(a < 2 && b < array.length) {
			if(thirdArr[a] != array[b]) {
				thirdArr[a+1] = array[b];
				a++;
			}
			b++;
		}
		if(a < 2) {
			//如果thirdArr只有两个元素
			return thirdArr[0] > thirdArr[1] ? thirdArr[0] : thirdArr[1];
		} else {
			//对thirdArr数组排序
			Arrays.sort(thirdArr); //升序
		}

		//对剩余数组进行比较
		while(b < array.length) {
			if(thirdArr[2] < array[b]) {
				//1.最大的数比较
				thirdArr[0] = thirdArr[1];
				thirdArr[1] = thirdArr[2];
				thirdArr[2] = array[b];
				b++;
				continue;
			}
			if(thirdArr[1] < array[b]) {
				//2.中间数比较
				thirdArr[0] = thirdArr[1];
				thirdArr[1] = array[b];
				b++;
				continue;
			}
			if(thirdArr[0] < array[b]) {
				//3.最小的数比较
				thirdArr[0] = array[b];
				b++;
				continue;
			}
			b++;
		}

		return thirdArr[0];
	}