run into:
1.撞到,例 run into a wall (撞到墙上)
2.陷入,例 run into trouble (陷入麻烦)
3.跑进,例 run into the store (跑进商店)
4.无意中遇见,例 I ran into her at the party.我是在派对上无意中遇见她的.
run across:
1.跑着穿过,例 run across the yard (跑着穿过院子)
2.无意中找到/遇见,语法类似 run into 的用法4.再给个例子：
I ran across her name in the telephone directory.
我无意中在电话簿里看见她的名字.