third week

Author: Shockang

Week_03/id_12/LeetCode_200_012.java

@@ -27,29 +27,29 @@
 
 class Solution {
 
-  int[] x = {1, 0, -1, 0};
-  int[] y = {0, -1, 0, 1};
+	int[] x = {1, 0, -1, 0};
+	int[] y = {0, -1, 0, 1};
 
-  public int numIslands(char[][] grid) {
-    int count = 0;
-    for (int i = 0; i < grid.length; i++) {
-      for (int j = 0; j < grid[i].length; j++) {
-        if (grid[i][j] == '1') {
-          count++;
-          sink(grid, i, j);
-        }
-      }
-    }
-    return count;
-  }
+	public int numIslands(char[][] grid) {
+		int count = 0;
+		for (int i = 0; i < grid.length; i++) {
+			for (int j = 0; j < grid[i].length; j++) {
+				if (grid[i][j] == '1') {
+					count++;
+					sink(grid, i, j);
+				}
+			}
+		}
+		return count;
+	}
 
-  private void sink(char[][] grid, int i, int j) {
-    if (i < 0 || j < 0 || i > grid.length - 1 || j > grid[i].length - 1 || grid[i][j] == '0') {
-      return;
-    }
-    grid[i][j] = '0';
-    for (int index = 0; index < 4; index++) {
-      sink(grid, i + x[index], j + y[index]);
-    }
-  }
+	private void sink(char[][] grid, int i, int j) {
+		if (i < 0 || j < 0 || i > grid.length - 1 || j > grid[i].length - 1 || grid[i][j] == '0') {
+			return;
+		}
+		grid[i][j] = '0';
+		for (int index = 0; index < 4; index++) {
+			sink(grid, i + x[index], j + y[index]);
+		}
+	}
 }

Week_03/id_12/LeetCode_210_012.java

@@ -0,0 +1,42 @@
+class Solution {
+
+	public int[] findOrder(int numCourses, int[][] prerequisites) {
+		List[] course = new List[numCourses];
+		int[] map = new int[numCourses];
+		List<Integer> resultList = new ArrayList<Integer>();
+		for (int i = 0; i < numCourses; i++) {
+			course[i] = new ArrayList<Integer>();
+		}
+		for (int i = 0; i < prerequisites.length; i++) {
+			course[prerequisites[i][0]].add(prerequisites[i][1]);
+		}
+		for (int i = 0; i < numCourses; i++) {
+			if (!dfs(course, i, resultList, map)) {
+				return new int[0];
+			}
+		}
+		int[] an = new int[resultList.size()];
+		for (int i = 0; i < resultList.size(); i++) {
+			an[i] = resultList.get(i);
+		}
+		return an;
+	}
+
+	private boolean dfs(List[] course, int req, List<Integer> list, int[] map) {
+		if (map[req] == 0) {
+			map[req] = 1;
+			for (int i = 0; i < course[req].size(); i++) {
+				if (!dfs(course, (int) course[req].get(i), list, map)) {
+					return false;
+				}
+			}
+			map[req] = 2;
+		} else if (map[req] == 1) {
+			return false;
+		} else if (map[req] == 2) {
+			return true;
+		}
+		list.add(req);
+		return true;
+	}
+}

Week_03/id_12/LeetCode_295_012.java

@@ -0,0 +1,21 @@
+class MedianFinder {
+
+	PriorityQueue<Integer> min = new PriorityQueue();
+	PriorityQueue<Integer> max = new PriorityQueue(1000, Collections.reverseOrder());
+
+	public void addNum(int num) {
+		max.offer(num);
+		min.offer(max.poll());
+		if (max.size() < min.size()) {
+			max.offer(min.poll());
+		}
+	}
+
+	public double findMedian() {
+		if (max.size() == min.size()) {
+			return (max.peek() + min.peek()) / 2.0;
+		} else {
+			return max.peek();
+		}
+	}
+};

Week_03/id_12/LeetCode_703_012.java

@@ -0,0 +1,23 @@
+class KthLargest {
+
+	final PriorityQueue<Integer> q;
+	final int k;
+
+	public KthLargest(int k, int[] a) {
+		this.k = k;
+		q = new PriorityQueue<>(k);
+		for (int n : a) {
+			add(n);
+		}
+	}
+
+	public int add(int n) {
+		if (q.size() < k) {
+			q.offer(n);
+		} else if (q.peek() < n) {
+			q.poll();
+			q.offer(n);
+		}
+		return q.peek();
+	}
+}

Week_03/id_12/NOTE.md

@@ -0,0 +1,2 @@
+# 学习笔记
+首先感觉作业题目越来越难了，第200题老师上课讲过了，对小岛沉没这种解法很有印象，也安装老师要求的用两个数组来表示方向，算是一次课堂温习；第210题，刚开始题目没有看清楚，不清楚第一个参数的作业，提醒自己以后审题一定要仔细，感觉这题的数据结构很像Java中的HashMap，可以借鉴着来理解；第295题感觉用优先队列来解决太巧妙了，学到了一招；第703题算是对优先队列的又一次灵活应用。