fd

Author: liwentian

ebook/graph/Graph.aux

@@ -66,8 +66,13 @@
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 \@writefile{toc}{\contentsline {subsubsection}{Solution I}{35}{section*.44}}
 \@writefile{toc}{\contentsline {subsubsection}{Solution II}{36}{section*.45}}
+\@writefile{toc}{\contentsline {section}{\numberline {1.19}Shortest Distance from All Buildings}{37}{section.1.19}}
+\@writefile{toc}{\contentsline {subsubsection}{Description}{37}{section*.46}}
+\@writefile{toc}{\contentsline {subsubsection}{Analysis}{37}{section*.47}}
+\@writefile{toc}{\contentsline {subsubsection}{Solution}{38}{section*.48}}
+\FN@pp@footnotehinttrue 
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ebook/graph/Graph.tex

@@ -1689,4 +1689,127 @@ \subsubsection{Solution II}
 }
 \end{Code}
 
-\newpage
+\newpage
+
+\section{Shortest Distance from All Buildings} %%%%%%%%%%%%%%%%%%%%%%
+
+\subsubsection{Description}
+
+You want to build a house on an empty land which reaches all buildings in the shortest amount of distance. You can only move up, down, left and right. You are given a 2D grid of values 0, 1 or 2, where:
+
+Each 0 marks an empty land which you can pass by freely.
+
+Each 1 marks a building which you cannot pass through.
+
+Each 2 marks an obstacle which you cannot pass through.
+
+For example, given three buildings at (0,0), (0,4), (2,2), and an obstacle at (0,2):
+
+\begin{Code}
+1 - 0 - 2 - 0 - 1
+|   |   |   |   |
+0 - 0 - 0 - 0 - 0
+|   |   |   |   |
+0 - 0 - 1 - 0 - 0
+\end{Code}
+
+The point (1,2) is an ideal empty land to build a house, as the total travel distance of 3+3+1=7 is minimal. So return 7.
+
+\textbf{Note:}
+
+There will be at least one building. If it is not possible to build such house according to the above rules, return -1.
+
+\subsubsection{Analysis}
+
+这道题思路是以所有建筑为根开始BFS，对所有覆盖到的点计算距离，
+
+每个空白点可能会同时被好几个建筑覆盖，所以其距离是叠加的，表示该点到那几个联通建筑的距离之和
+
+最后遍历所有空白点，求距离和最小的，同时能联通所有建筑的
+
+\newpage
+
+\subsubsection{Solution}
+
+\begin{Code}
+/**
+ * 1, 注意当没有结果时返回-1，而不是INT_MAX
+ * 2, 要保证参考点能通往所有建筑，所以要统计建筑数
+ * 3， bfs时要注意边界且别重复访问了
+ */
+public int shortestDistance(int[][] grid) {
+    if (grid.length == 0) {
+        return -1;
+    }
+    int row = grid.length, col = grid[0].length;
+
+    int[][] dis = new int[row][col];
+    int[][] building = new int[row][col];
+    int buildings = 0;
+
+    for (int i = 0; i < row; i++) {
+        for (int j = 0; j < col; j++) {
+            if (grid[i][j] != 1) {
+                continue;
+            }
+
+            buildings++;
+            bfs(grid, dis, building, i, j);
+        }
+    }
+
+    int shortest = Integer.MAX_VALUE;
+    for (int i = 0; i < row; i++) {
+        for (int j = 0; j < col; j++) {
+            if (grid[i][j] == 0 && building[i][j] == buildings) {
+                shortest = Math.min(shortest, dis[i][j]);
+            }
+        }
+    }
+    return shortest == Integer.MAX_VALUE ? -1 : shortest;
+}
+\end{Code}
+
+\newpage
+
+\begin{Code}
+private void bfs(int[][] grid, int[][] dis, int[][] building, int i, int j) {
+    Queue<int[]> queue = new LinkedList<>();
+    queue.add(new int[] {i, j});
+
+    Queue<int[]> next = new LinkedList<>();
+
+    boolean[][] visited = new boolean[grid.length][grid[0].length];
+
+    int level = 0;
+
+    while (!queue.isEmpty()) {
+        int[] pos = queue.poll();
+        int x0 = pos[0], y0 = pos[1];
+
+        dis[x0][y0] += level;
+        building[x0][y0]++;
+
+        int[] dx = {1, -1, 0, 0}, dy = {0, 0, 1, -1};
+
+        for (int m = 0; m < dx.length; m++) {
+            int x = x0 + dx[m], y = y0 + dy[m];
+
+            if (x < 0 || x >= grid.length || y < 0 || y >= grid[0].length) {
+                continue;
+            }
+
+            if (grid[x][y] == 0 && !visited[x][y]) {
+                visited[x][y] = true;
+                next.offer(new int[]{x, y});
+            }
+        }
+
+        if (queue.isEmpty()) {
+            queue.addAll(next);
+            next.clear();
+            level++;
+        }
+    }
+}
+\end{Code}

ebook/graph/leetcode-graph.log

@@ -1,4 +1,4 @@
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+This is XeTeX, Version 3.14159265-2.6-0.99996 (TeX Live 2016) (preloaded format=xelatex 2017.9.4)  7 SEP 2017 22:17
 entering extended mode
  restricted \write18 enabled.
  %&-line parsing enabled.
@@ -1929,7 +1929,7 @@ up above has ended a previous alignment prematurely,
 you're probably due for more error messages, and you
 might try typing `S' now just to see what is salvageable.
 
-[32] [33] [34] [35] [36])
+[32] [33] [34] [35] [36] [37] [38]) [39]
 No file leetcode-graph.ind.
 Package atveryend Info: Empty hook `BeforeClearDocument' on input line 44.
 Package atveryend Info: Empty hook `AfterLastShipout' on input line 44.
@@ -1939,12 +1939,12 @@ Package atveryend Info: Empty hook `AtEndAfterFileList' on input line 44.
 Package atveryend Info: Empty hook `AtVeryVeryEnd' on input line 44.
  ) 
 Here is how much of TeX's memory you used:
- 29194 strings out of 493591
- 554153 string characters out of 6143547
- 576144 words of memory out of 5000000
- 32225 multiletter control sequences out of 15000+600000
+ 29204 strings out of 493591
+ 554870 string characters out of 6143547
+ 579531 words of memory out of 5000000
+ 32235 multiletter control sequences out of 15000+600000
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  1347 hyphenation exceptions out of 8191
  65i,11n,77p,10420b,474s stack positions out of 5000i,500n,10000p,200000b,80000s
 
-Output written on leetcode-graph.pdf (38 pages).
+Output written on leetcode-graph.pdf (41 pages).

ebook/graph/leetcode-graph.out

@@ -17,3 +17,4 @@
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ebook/graph/leetcode-graph.pdf

@@ -61,3 +61,7 @@
 \contentsline {subsubsection}{Description}{34}{section*.43}
 \contentsline {subsubsection}{Solution I}{35}{section*.44}
 \contentsline {subsubsection}{Solution II}{36}{section*.45}
+\contentsline {section}{\numberline {1.19}Shortest Distance from All Buildings}{37}{section.1.19}
+\contentsline {subsubsection}{Description}{37}{section*.46}
+\contentsline {subsubsection}{Analysis}{37}{section*.47}
+\contentsline {subsubsection}{Solution}{38}{section*.48}