package org.ooc.frontend;

/**
 * Computes the Levenshtein distance between two strings
 * @author Michael Gilleland
 */
public class Levenshtein {

	// ****************************
	// Get minimum of three values
	// ****************************

	protected static int min(int a, int b, int c) {
		int mi;

		mi = a;
		if (b < mi) {
			mi = b;
		}
		if (c < mi) {
			mi = c;
		}
		return mi;

	}

	// *****************************
	// Compute Levenshtein distance
	// *****************************

	public static int distance(String s, String t) {
		int d[][]; // matrix
		int n; // length of s
		int m; // length of t
		int i; // iterates through s
		int j; // iterates through t
		char s_i; // ith character of s
		char t_j; // jth character of t
		int cost; // cost

		// Step 1

		n = s.length();
		m = t.length();
		if (n == 0) {
			return m;
		}
		if (m == 0) {
			return n;
		}
		d = new int[n + 1][m + 1];

		// Step 2

		for (i = 0; i <= n; i++) {
			d[i][0] = i;
		}

		for (j = 0; j <= m; j++) {
			d[0][j] = j;
		}

		// Step 3

		for (i = 1; i <= n; i++) {

			s_i = s.charAt(i - 1);

			// Step 4

			for (j = 1; j <= m; j++) {

				t_j = t.charAt(j - 1);

				// Step 5

				if (s_i == t_j) {
					cost = 0;
				} else {
					cost = 1;
				}

				// Step 6
				
				d[i][j] = min(d[i - 1][j] + 1, d[i][j - 1] + 1,
						d[i - 1][j - 1] + cost);

			}

		}

		// Step 7
		
		return d[n][m];

	}

}