From 0b897ff02472d64d651c6a2e7d5f00311063a9fc Mon Sep 17 00:00:00 2001
From: teivaz <teivaz@rambler.ru>
Date: Wed, 13 Jan 2016 13:37:26 +0200
Subject: [PATCH 1/2] Better solution for 5_7 with xor sum and without
 recursion

---
 c++/Chapter 5/Question5_7.cpp | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/c++/Chapter 5/Question5_7.cpp b/c++/Chapter 5/Question5_7.cpp
index 8b0665a1..524acd5a 100644
--- a/c++/Chapter 5/Question5_7.cpp	
+++ b/c++/Chapter 5/Question5_7.cpp	
@@ -6,6 +6,28 @@ int fetchBit(int bit, int no){
 	return (no&1);
 }
 
+int findMissingWithXor(int A[], int N){
+    int n = 1;
+    int xorTarget = 1;
+    int xorActual = 0;
+    
+    int maxBytes = sizeof(int); // optimize to number of significant bits in N
+    for(int i = 0; i < N; ++i){
+        
+        // Find the XOR sum of elements 0...N
+        // Possibly can optimzie without loop
+        xorTarget ^= ++n;
+        
+        // Sweep throug each bit (preferably significant)
+        // and calculate XOR sum of that
+        for(int j = 0; j < maxBytes; ++j){
+            xorActual ^= (fetchBit(A[i], j) << j);
+        }
+    }
+    // XOR target and actual sums to find missing
+    return xorActual ^ xorTarget;
+}
+
 int findMissingUtils(int A[], int n, int col){
 	if(n <2){
 		return 0;
@@ -39,6 +61,7 @@ void findMissing(int A[], int n){
 
 int main(){
 	int A[] = {2, 5, 6, 0, 1, 3, 4, 8, 9, 10, 11, 12};
-	findMissing(A, 12);
+	//findMissing(A, 12);
+    findMissingWithXor(A, 12);
 	return 0;
 }
\ No newline at end of file

From 057db051b9db307afb4a10d3e2af373ab2e4e365 Mon Sep 17 00:00:00 2001
From: teivaz <teivaz@rambler.ru>
Date: Wed, 13 Jan 2016 16:02:33 +0200
Subject: [PATCH 2/2] Solution for 5_8

---
 c++/Chapter 5/Question5_8.cpp | 46 ++++++++++++++++++++++++++++++++++-
 1 file changed, 45 insertions(+), 1 deletion(-)

diff --git a/c++/Chapter 5/Question5_8.cpp b/c++/Chapter 5/Question5_8.cpp
index 35b2d3e8..33967f28 100644
--- a/c++/Chapter 5/Question5_8.cpp	
+++ b/c++/Chapter 5/Question5_8.cpp	
@@ -1,9 +1,53 @@
 #include<iostream>
 using namespace std;
 
+void PrintScreen(unsigned char buffer[], int width, int height){
+    int byteWidth = width / 8;
+    for(int row = 0; row < height; ++row){
+        for(int column = 0; column < byteWidth; ++column){
+            int index = row * byteWidth + column;
+            char block = buffer[index];
+            for(int i = 7; i >= 0; --i){
+                if( (block >> i) & 1){
+                    cout << '.';
+                }
+                else{
+                    cout << ' ';
+                }
+            }
+        }
+        cout << '\n';
+    }
+}
 
+void SetBit(unsigned char& byte, int bit){
+    byte |= 1 << bit;
+}
 
-int main(){
+void DrawHorizontalLine(unsigned char buffer[], int bufferLength, int width, int x1, int x2, int y){
+    int x = width * y + x1;
+    int end = width * y + x2;
+    while(x < end){
+        int byteIndex = x / 8;
+        int bit = x - byteIndex * 8;
+        SetBit(buffer[byteIndex], 7 - bit);
+        ++x;
+    }
+}
 
+int main(){
+    unsigned char screen[] = {
+        0x80, 0x01,
+        0x40, 0x02,
+        0x20, 0x04,
+        0x10, 0x08,
+        0x08, 0x10,
+        0x04, 0x20,
+        0x02, 0x40,
+        0x01, 0x80
+    };
+    PrintScreen(screen, 16, 8);
+    DrawHorizontalLine(screen, 2 * 8, 16, 5, 9, 2);
+    PrintScreen(screen, 16, 8);
 	return 0;
 }
\ No newline at end of file