The problem requires finding the lexicographically smallest string that can be formed by starting from any leaf node in a binary tree and traversing up to the root.

输入: S = "xy "，T = "axy" **输出:**是 **说明:**把 yx 重新排列成 xy，axy 重新排列成 yxa。然后，xy < yxa。 // Java program for the above ...