Openjudge1388 Lake Counting【DFS/Flood Fill】
阿新 • • 發佈：2017-11-12
title lac n+1 其他 content problem not pre any
http://blog.csdn.net/c20182030/article/details/52327948
1388:Lake Counting
- 總時間限制:
- 1000ms
- 內存限制:
- 65536kB
- 描述
- Due to recent rains, water has pooled in various places in Farmer John‘s field, which is represented by a rectangle of N x M (1 <= N <= 100; 1 <= M <= 100) squares. Each square contains either water (‘W‘) or dry land (‘.‘). Farmer John would like to figure out how many ponds have formed in his field. A pond is a connected set of squares with water in them, where a square is considered adjacent to all eight of its neighbors.
Given a diagram of Farmer John‘s field, determine how many ponds he has. - 輸入
- * Line 1: Two space-separated integers: N and M
* Lines 2..N+1: M characters per line representing one row of Farmer John‘s field. Each character is either ‘W‘ or ‘.‘. The characters do not have spaces between them. - 輸出
- * Line 1: The number of ponds in Farmer John‘s field.
- 樣例輸入
-
10 12 W........WW. .WWW.....WWW ....WW...WW. .........WW. .........W.. ..W......W.. .W.W.....WW. W.W.W.....W. .W.W......W. ..W.......W.
- 樣例輸出
-
3
- 提示
- OUTPUT DETAILS:
There are three ponds: one in the upper left, one in the lower left,and one along the right side. - 來源
- USACO 2004 Novembe
- 題目大意
- 大雨過後，農夫John的農場
被水淹沒不知所措有了積水，農場地圖中‘W’代表積水，‘.‘代表幹燥的土地。八連通的積水在同一個水窪裏。農夫John想知道農場裏有多少水窪。 - 這是一道搜索題。與其他搜索題一樣，都是不斷地搜索，直到達到目的。但是，這道題的目的是什麽呢？
- 目的是求出有多少水窪，如果遞歸的話，怎麽才能知道求出了數量呢？
- 所以這樣，不能單純的只調用一次函數（主程序中），否則最多只會找出一個水窪。
- 我一開始是這樣想的，把每個水窪只留下一個W，其余換成幹燥，最後再看有幾個W。可是這樣搜索的時候，留下的W也會被搜到，搜到就會變成‘.‘，答案就會是0。為了避免這個問題，需要設立一個輔助數組或者把這個W換成另一個字符，但是這樣既浪費時間也浪費空間（還浪費我的腦容量）。
- 於是我把函數寫在循環裏，把一個水窪消滅幹凈後，水窪數量就加1。我用DFS，BFS實現了這個想法。
Openjudge1388 Lake Counting【DFS/Flood Fill】