I found it difficult. 等不等于 i found it is/was difficult?

应该等于
find的用法
find+it+adj
find(that可以省略)+句子

两句是相等的
find+it+adj+to do
find (that) +宾语从句

两个都是可以的,意思相同^_^

I found it difficult to solve the problem. 等不等于 i found it is/was difficult to solve the problem?

i found it difficult.=i found (that) it is/was difficult (to solve the problem).
但是，i found it difficult to solve the problem是不对的，"to solve the problem"我不知道它是句子的什么成分，是有find+it+adj.的用法，但是后面没有任何其他内容。
分析一下i found it difficult to solve the problem.的结构：i是主语，found是谓语，it是宾语，difficult是定语用于修饰it。可是to solve the problem是状语吗？是补语吗？都不是，放在这里句子就错了。