diff --git a/functions.py b/functions.py
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--- /dev/null
+++ b/functions.py
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+
+#!/usr/bin/python
+def islandPerimeter(grid):
+    """
+    The solution to today's leetcode challenge.
+    :type grid: List[List[int]]
+    :rtype: int
+    """
+    
+    leni = len(grid)
+    lenj = len(grid[0])
+
+    def countCell(i,j):
+        if not grid[i][j]:
+            return 0
+        borders = 4
+        if i>0 and grid[i-1][j]: borders -= 1
+        if i<(leni-1) and grid[i+1][j]: borders -= 1
+        if j<(lenj-1) and grid[i][j+1]: borders -= 1
+        if j>0 and grid[i][j-1]: borders -= 1
+        return borders
+    
+    return sum([countCell(i,j) for i in range(leni) for j in range(lenj)])
+
+
+"""This program uses scipy to integrate and plot the results of a basic SIR model"""
+
+
+from scipy import * 
+from scipy.integrate import *
+from pylab import *
+
+#Define Constants
+beta=2.0
+gamma=.8
+init=array([0.95,0.05,0.0])
+finalTime=20.0
+time=arange(0,finalTime, 0.01)
+
+def derv(x,t):
+    """Computes the derv operator for the basic sir model"""
+
+    y=zeros(3); 
+    y[0]=-beta*x[0]*x[1]
+    y[1]=beta*x[0]*x[1]-gamma*x[1]
+    y[2]=gamma*x[1]
+    return(y)
+
+
+r=odeint(derv, init, time)
+
+plot(time, r[:,0], "r", time, r[:,1], "g", time, r[:,2], "b")
+legend(("Susceptible","Infected","Recovered"), loc=0)
+ylabel("Number of People")
+xlabel("Time")
+title("SIR Model")
+
+show()
+
+#!/usr/bin/env python2
+# -*- coding: utf-8 -*-
+"""
+Created on Tue Apr  4 10:53:33 2017
+
+@author: zhihuixie
+"""
+
+def countPrimes(self, n):
+    """
+    :type n: int
+    :rtype: int
+    """
+    if n < 3:
+        return 0
+    arr = [True]*n
+    arr[0] = arr[1] = False
+    # optimization - any number can be divide by i*(i+n) is not a primer
+    for i in xrange(2, int(n**0.5) + 1):
+        if arr[i]:
+            arr[i*i : n : i] = [False]*len(arr[i*i : n : i])
+    return sum(arr)