Create README.md
Update README.md

add screenshot
update readme.
update Python version of Single Number.
add solution for Valid-Number. Resort the list.txt.
add Solutions for Sqrt.
update list.txt
add classpath support in Makefile
add solutions for Populating-Next-Right-Pointers-in-Each-Node .
optimize codes for Populating-Next-Right-Pointers-in-Each-Node
optimize codes for Populating-Next-Right-Pointers-in-Each-Node
add solutions for Find-Minimum-in-Rotated-Sorted-Array
add solutions for Path-Sum
add solutions for Path-Sum-II
add solution for Minimum-Path-Sum.
update list.txt.
add solutions for Two-Sum
add solutions for Unique-Paths
add java version for Sort-List
update namespace usage.