algorithm-class/MCA算法突击课/第02期/mca_01/Code04_NumberOfIslands.java

package 第02期.mca_01;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Stack;

// 本题为leetcode原题
// 测试链接：https://leetcode.cn/problems/number-of-islands/
// 所有方法都可以直接通过
public class Code04_NumberOfIslands {

	public static int numIslands3(char[][] board) {
		int islands = 0;
		for (int i = 0; i < board.length; i++) {
			for (int j = 0; j < board[0].length; j++) {
				if (board[i][j] == '1') {
					islands++;
					infect(board, i, j);
				}
			}
		}
		return islands;
	}

	// 从(i,j)这个位置出发，把所有练成一片的'1'字符，变成0
	public static void infect(char[][] board, int i, int j) {
		if (i < 0 || i == board.length || j < 0 || j == board[0].length || board[i][j] != '1') {
			return;
		}
		board[i][j] = 0;
		infect(board, i - 1, j);
		infect(board, i + 1, j);
		infect(board, i, j - 1);
		infect(board, i, j + 1);
	}

	public static int numIslands1(char[][] board) {
		int row = board.length;
		int col = board[0].length;
		Dot[][] dots = new Dot[row][col];
		List<Dot> dotList = new ArrayList<>();
		for (int i = 0; i < row; i++) {
			for (int j = 0; j < col; j++) {
				if (board[i][j] == '1') {
					dots[i][j] = new Dot();
					dotList.add(dots[i][j]);
				}
			}
		}
		UnionFind1<Dot> uf = new UnionFind1<>(dotList);
		for (int j = 1; j < col; j++) {
			// (0,j)  (0,0)跳过了  (0,1) (0,2) (0,3)
			if (board[0][j - 1] == '1' && board[0][j] == '1') {
				uf.union(dots[0][j - 1], dots[0][j]);
			}
		}
		for (int i = 1; i < row; i++) {
			if (board[i - 1][0] == '1' && board[i][0] == '1') {
				uf.union(dots[i - 1][0], dots[i][0]);
			}
		}
		for (int i = 1; i < row; i++) {
			for (int j = 1; j < col; j++) {
				if (board[i][j] == '1') {
					if (board[i][j - 1] == '1') {
						uf.union(dots[i][j - 1], dots[i][j]);
					}
					if (board[i - 1][j] == '1') {
						uf.union(dots[i - 1][j], dots[i][j]);
					}
				}
			}
		}
		return uf.sets();
	}

	public static class Dot {

	}

	public static class Node<V> {

		V value;

		public Node(V v) {
			value = v;
		}

	}

	public static class UnionFind1<V> {
		public HashMap<V, Node<V>> nodes;
		public HashMap<Node<V>, Node<V>> parents;
		public HashMap<Node<V>, Integer> sizeMap;

		public UnionFind1(List<V> values) {
			nodes = new HashMap<>();
			parents = new HashMap<>();
			sizeMap = new HashMap<>();
			for (V cur : values) {
				Node<V> node = new Node<>(cur);
				nodes.put(cur, node);
				parents.put(node, node);
				sizeMap.put(node, 1);
			}
		}

		public Node<V> findFather(Node<V> cur) {
			Stack<Node<V>> path = new Stack<>();
			while (cur != parents.get(cur)) {
				path.push(cur);
				cur = parents.get(cur);
			}
			while (!path.isEmpty()) {
				parents.put(path.pop(), cur);
			}
			return cur;
		}

		public void union(V a, V b) {
			Node<V> aHead = findFather(nodes.get(a));
			Node<V> bHead = findFather(nodes.get(b));
			if (aHead != bHead) {
				int aSetSize = sizeMap.get(aHead);
				int bSetSize = sizeMap.get(bHead);
				Node<V> big = aSetSize >= bSetSize ? aHead : bHead;
				Node<V> small = big == aHead ? bHead : aHead;
				parents.put(small, big);
				sizeMap.put(big, aSetSize + bSetSize);
				sizeMap.remove(small);
			}
		}

		public int sets() {
			return sizeMap.size();
		}

	}

	public static int numIslands2(char[][] board) {
		int row = board.length;
		int col = board[0].length;
		UnionFind2 uf = new UnionFind2(board);
		for (int j = 1; j < col; j++) {
			if (board[0][j - 1] == '1' && board[0][j] == '1') {
				uf.union(0, j - 1, 0, j);
			}
		}
		for (int i = 1; i < row; i++) {
			if (board[i - 1][0] == '1' && board[i][0] == '1') {
				uf.union(i - 1, 0, i, 0);
			}
		}
		for (int i = 1; i < row; i++) {
			for (int j = 1; j < col; j++) {
				if (board[i][j] == '1') {
					if (board[i][j - 1] == '1') {
						uf.union(i, j - 1, i, j);
					}
					if (board[i - 1][j] == '1') {
						uf.union(i - 1, j, i, j);
					}
				}
			}
		}
		return uf.sets();
	}

	public static class UnionFind2 {
		private int[] parent;
		private int[] size;
		private int[] help;
		private int col;
		private int sets;

		public UnionFind2(char[][] board) {
			col = board[0].length;
			sets = 0;
			int row = board.length;
			int len = row * col;
			parent = new int[len];
			size = new int[len];
			help = new int[len];
			for (int r = 0; r < row; r++) {
				for (int c = 0; c < col; c++) {
					if (board[r][c] == '1') {
						int i = index(r, c);
						parent[i] = i;
						size[i] = 1;
						sets++;
					}
				}
			}
		}

		// (r,c) -> i
		private int index(int r, int c) {
			return r * col + c;
		}

		// 原始位置 -> 下标
		private int find(int i) {
			int hi = 0;
			while (i != parent[i]) {
				help[hi++] = i;
				i = parent[i];
			}
			for (hi--; hi >= 0; hi--) {
				parent[help[hi]] = i;
			}
			return i;
		}

		public void union(int r1, int c1, int r2, int c2) {
			int i1 = index(r1, c1);
			int i2 = index(r2, c2);
			int f1 = find(i1);
			int f2 = find(i2);
			if (f1 != f2) {
				if (size[f1] >= size[f2]) {
					size[f1] += size[f2];
					parent[f2] = f1;
				} else {
					size[f2] += size[f1];
					parent[f1] = f2;
				}
				sets--;
			}
		}

		public int sets() {
			return sets;
		}

	}

}