尋找中位數(Java)

問題描述：
給定兩個有序數組arr1和arr2，兩個數組長度都爲N（N>0），求兩個數組中所有數的上中位數，要求：時間複雜度爲O（logN）。
eg: a1={1,2,3,4}; a2={5,6,7,8}。返回值爲4。

public class Solution2 {
	public static int findMid(int[] a1, int start1, int end1, int[] a2, int start2, int end2) {
		int i = start1 + (end1-start1)/2;
		int j = start2 + (end2-start2)/2;
		if(i == a1.length-1) return a1[i]; //a1數組中的數都小於a2[0]中的數，返回最末尾的值
		if(j == a2.length-1) return a2[j]; //a2數組中的數都小於a1[0]
		
		if(a1[i]<=a2[j] && a1[i+1]>=a2[j]) //a2[j]插入第N個位置
			return a2[j];
		if(a2[j]<=a1[i] && a2[j+1]>=a1[i]) //a1[i]插入第N個位置
			return a1[i];
		
		if(a1[i]<a2[j] && a1[i+1]<a2[j]){ //在a1的後半段和a2的前半段
			return findMid(a1,i+1,end1,a2,start2,j-1);
		}
		if(a2[j]<a1[i] && a2[j+1]<a1[i]){
			return findMid(a1,start1,i-1,a2,j+1,end2);
		}
		return -1;
		
	}

	public static void main(String[] args) {
		//int[] a1 = {1,2,3,4};
		//int[] a2 = {5,6,7,8};
		
		//int[] a1 = {1,2,3,4,9};
		//int[] a2 = {5,6,7,8,10};
		
		//int[] a1 = {1,2,5,6,9};
		//int[] a2 = {3,4,5,7,8};
		
		int[] a1 = {1,2,3};
		int[] a2 = {1,2,3};
		
		System.out.println(findMid(a1,0,a1.length-1,a2,0,a2.length-1));
		

	}

}