[ALGO] Is Binary Search Tree

Given a binary tree, verify if it is Binary Search Tree

[ALGO] Find the string in 2 dimensional matrix

Given a 2-dim matrix of characters 'm' and a string 's' - find if the string 's' is present in the matrix. Only characters in the neighboring cells of a cell can contribute to the string.

For example, for the case below B,D,F,G are neighbors of X. From 'X' possible strings (or substrings) are XB, XD, XF, XH.
|-----|-----|-----|
|  A  |  B  |  C  |
|-----|-----|-----|
|  H  |  X  |  D  |
|-----|-----|-----|
|  G  |  F  |  E  |
|-----|-----|-----|

Finally, an example. Given the matrix

(0,0)
    |-----|-----|-----|-----|
    |  y  |  a  |  a  |  o  |
    |-----|-----|-----|-----|
    |  a  |  o  |  a  |  o  |
    |-----|-----|-----|-----|
    |  y  |  a  |  o  |  o  |
    |-----|-----|-----|-----|
    |  h  |  a  |  a  |  o  |
    |-----|-----|-----|-----|
    |  y  |  a  |  h  |  o  |
    |-----|-----|-----|-----|
                            (3,3)

and asked to check for the string 'yahoo' the solution is true :
y - (3,0)
a - (3,1)
h - (3,2)
o - (3,3)
o - (2,3)