[100, 100, 300],[100, 200, 200]
100
合并体重 = [100,100,100,200,200,300] ,众数为100,返回100
[100,100,200,200],[300,300,400,400]
400
合并体重 = [100,100,200,200,300,300,400,400] ,众数为100,200,300和400,返回400
weightsA.length == mweightsB.length == n0 0 1 0