dp and some other stuff

213_HouseRobberII.cpp

@@ -0,0 +1,55 @@
+#include <iostream>
+#include <vector>
+
+using namespace std;
+
+int MaxRingLoot(const vector<int>& nums)
+{
+	//take maximum of loot from 0 to n-2 and 1 to n-1
+
+	//case where 0 is picked
+
+	int lootMinusTwo =0;
+	int lootMinusOne =nums.front();
+
+	for(int i =1; i<nums.size()-1; i++)
+	{
+		int bestLoot = max(nums[i]+lootMinusTwo,lootMinusOne);
+		lootMinusTwo = lootMinusOne;
+		lootMinusOne = bestLoot;
+	}
+
+	int bestLoot = lootMinusOne;
+
+
+	//case where 0 is skipped
+	lootMinusOne = nums[1];
+	lootMinusTwo = 0;
+
+	for(int i = 2; i<nums.size(); i++)
+	{
+		int best = max(nums[i]+lootMinusTwo,lootMinusOne);
+		lootMinusTwo = lootMinusOne;
+		lootMinusOne = best;
+	}
+
+	bestLoot = max(bestLoot,lootMinusOne);
+
+	return bestLoot;
+
+}
+
+int main()
+{
+	int nLength;
+	cin >> nLength;
+
+	vector<int> vecHouses(nLength);
+
+	for(int i =0; i<vecHouses.size(); i++)
+		cin >> vecHouses[i];
+
+	cout << "Max ring loot is " << MaxRingLoot(vecHouses) << endl;
+	return 0;
+
+}

54_SpiralMatrix.cpp

@@ -0,0 +1,83 @@
+#include <iostream>
+#include <vector>
+
+using namespace std;
+
+vector<int> SpiralTraversal(vector<vector<int>> matrix)
+{
+	//sanity checks
+	if (matrix.empty()) return vector<int>();
+
+	//keep track of move direction and available steps
+	bool movHz = true; //moving horizontally
+	bool movRv = false; //moving vertically
+	int hzMaxSteps = matrix[0].size(); //total horizontal steps
+	int vtMaxSteps = matrix.size()-1; //total vertical steps
+	int i=0,j=0; //starting pos
+
+	vector<int> vecSpiral;
+
+	while(true)
+	{
+		//no more steps available
+		if( (movHz ? hzMaxSteps : vtMaxSteps) <= 0)
+			break;
+
+		//move ahead available number of steps in the correct direction
+		if (movHz)
+			for(int x =0; x<hzMaxSteps; x++)
+				vecSpiral.push_back(movRv ? matrix[i][j--] : matrix[i][j++]);
+		else
+			for(int x =0; x<vtMaxSteps; x++)
+				vecSpiral.push_back(movRv ? matrix[i--][j] : matrix[i++][j]);
+
+		//fix overshoot
+		if (movHz)
+			movRv ? j++ : j--;
+		else
+			movRv ? i++ : i--;
+
+		//update max steps
+		movHz ? hzMaxSteps-- : vtMaxSteps--;
+
+
+		//change direction
+		movHz = !movHz;
+
+		//change reverse or forward order
+		//if going from v to h
+		movRv = movHz ? !movRv : movRv;
+
+		//change indices to new starting position
+		if (movHz)
+			movRv ? j-- : j++;
+		else
+			movRv ? i-- : i++;
+	}
+
+	return vecSpiral;
+
+}
+
+int main()
+{
+	int m,n;
+
+	cin >> m;
+	cin >> n;
+
+	vector<vector<int>> matrix(m,vector<int>(n));
+
+	for (int i =0; i<m; i++)
+	{
+		for(int j=0; j<n; j++)
+			cin >> matrix[i][j];
+	}
+
+	vector<int> vecResult = SpiralTraversal(matrix);
+
+	for(auto & num : vecResult)
+		cout << num <<  " ";
+	cout << endl;
+	return 0;
+}

62_UniquePaths.cpp

@@ -0,0 +1,35 @@
+#include <vector>
+#include <cstdlib>
+#include <iostream>
+
+using namespace std;
+
+int CountUniqueWays(int m, int n)
+{
+	//can either come from above or from left
+	//count both
+	vector<int> vecWays(m);
+	for(int i =0; i<m; i++)
+		vecWays[i] = 1; //exactly one way to get to anywhere in the top row
+
+	//calculate rest
+	for(int i =1; i<n; i++)
+	{
+		//take sum of total ways from top and left
+		//i.e. i-1,j and i,j-1
+		for(int j =0; j<m; j++)
+			vecWays[j] += (j>0?vecWays[j-1]:0);
+	}
+
+	return vecWays.back();
+}
+
+int main()
+{
+	int m;
+	int n;
+	cin >> m;
+	cin >> n;
+	printf("number of ways of getting to %d,%d from %d,%d are %d\n",0,0,m-1,n-1,CountUniqueWays(m,n));
+    	return 0;	
+}

91_DecodeWays.cpp

@@ -0,0 +1,47 @@
+#include <iostream>
+#include <vector>
+
+
+using namespace std;
+
+
+int DecodeWays(const string & strMessage)
+{
+	if (strMessage.empty()) return 0;
+
+	//can decode substrign upto ith position if there is a valid string decodign at i-1 or i-2
+	//and ith or ith+i-1th characters comprise valid encoded letters
+	//for empty string 
+	int waysMinusOne = 1;
+	int waysMinusTwo = 0;
+
+	for(int i=0; i<strMessage.length(); i++)
+	{
+		int encodingValue = (strMessage[i]-'0') + (i>0?(strMessage[i-1]-'0')*10:0);
+
+		int currentWays = 0;
+		//no of ways if valid decoding at i-1 and this character is a valid letter
+		if (strMessage[i] <= '9' && strMessage[i] >= '1')
+			currentWays = waysMinusOne;
+
+		//no of ways if valid decoding at i-2 and this and the last character comprise of a valid two digit encoded letter
+		//only count the cases where two letter decoding
+		if (encodingValue >= 10 && encodingValue <= 26)
+			currentWays += waysMinusTwo;
+
+
+		waysMinusTwo = waysMinusOne;
+		waysMinusOne = currentWays;
+	}
+
+	return waysMinusOne;
+}	
+
+int main()
+{
+	string strMessage;
+	getline(cin, strMessage);
+
+	cout << "Number of possible ways of decoding string are " << DecodeWays(strMessage) << endl;
+}
+