java Algorithms.txt

Reverse the given Array without using built in function

public class ReverseArray {
    static int [] a;
    public static void reverseIteration(){
        int start =0;
        int end  = a.length-1;
        while(start<=end){
            int temp = a[start];
            a[start] = a[end];
            a[end] = temp;
            start++;
            end--;
        }
    }

    public static void reverseRecursive(int start, int end){
        if(start<=end){
            int temp = a[start];
            a[start] = a[end];
            a[end] = temp;
            start++;
            end--;
            reverseRecursive(start, end);
        }
    }
    public static void main(String[] args) {
        a = new int []{1,2,3,4,5};
        System.out.println("Original Array" + Arrays.toString(a));
        reverseIteration();
        System.out.println("Reversed - Array(Iteration):" + Arrays.toString(a));
        reverseRecursive(0,a.length-1);
        System.out.println("Reversed Again - Array(Recursion):" + Arrays.toString(a));
    }
}


Print All Elements of Two Dimensional Array in Spiral:
public class Print2DArrayInSpiral {

	public int arrA[][] = { { 1, 2, 3, 4, 5 }, { 18, 19, 20, 21, 6 },
			{ 17, 28, 29, 22, 7 }, { 16, 27, 30, 23, 8 },
			{ 15, 26, 25, 24, 9 }, { 14, 13, 12, 11, 10 } };

	public int printSpiral(int row_S, int row_E, int col_S, int col_E,
			boolean reverse, boolean rowPrint) {

		if (row_S > row_E && col_S > col_E) {
			return 1;
		}
		if (rowPrint == false) {
			if (reverse == false) {
				for (int i = col_S; i <= col_E; i++) {
					System.out.print(" " + arrA[row_S][i]);
				}
			}
			row_S++;
			rowPrint = true;
			reverse = false;
		}
		if (rowPrint == true) {
			if (reverse == false) {
				for (int i = row_S; i <= row_E; i++) {
					System.out.print(" " + arrA[i][col_E]);
				}
			}
			col_E--;
			rowPrint = false;
			reverse = true;
		}
		if (rowPrint == false) {
			if (reverse == true) {
				for (int i = col_E; i >= col_S; i--) {
					System.out.print(" " + arrA[row_E][i]);
				}
			}
			row_E--;
			rowPrint = true;
			reverse = true;
		}
		if (rowPrint == true) {
			if (reverse == true) {
				for (int i = row_E; i >= row_S; i--) {
					System.out.print(" " + arrA[i][col_S]);
				}
			}
			col_S++;
			rowPrint = false;
			reverse = false;
		}
		printSpiral(row_S, row_E, col_S, col_E, reverse, rowPrint);
		return 0;
	}

	public static void main(String args[]) {
		Print2DArrayInSpiral p = new Print2DArrayInSpiral();
		p.printSpiral(0, 5, 0, 4, false, false);
	}

}

Longest Common Substring
public class LongestCommonSubString {

	public static int find(char [] A, char [] B){
		int [][]LCS = new int [A.length+1][B.length+1];
		// if A is null then LCS of A, B =0
		for(int i=0;i<=B.length;i++){
			LCS[0][i]=0;
		}
		
		// if B is null then LCS of A, B =0
		for(int i=0;i<=A.length;i++){ 
			LCS[i][0]=0;
		}
		
		//fill the rest of the matrix
		for(int i=1;i<=A.length;i++){
			for(int j=1;j<=B.length;j++){
				if(A[i-1]==B[j-1]){
					LCS[i][j] =  LCS[i-1][j-1] +1;
				}else{
					LCS[i][j] = 0;					
				}
			}
		}	
		int result = -1;
		for(int i=0;i<=A.length;i++){
			for(int j=0;j<=B.length;j++){
				if(result<LCS[i][j]){
					result = LCS[i][j];
				}
			}
		}	
		return result;
	}
	public static void main(String[] args) {
		String A = "tutorialhorizon";
		String B = "dynamictutorialProgramming";		
		System.out.println("LCS length : " + find(A.toCharArray(), B.toCharArray()));
	}
}