火力网3 （学习总结）

今天用java完整的写了火力网的代码，第一次想zju递交代码，很爽居然通过了，令我很开心！

以前申请北大的online judge一直不给我递交权限，还是家乡的学校好。哈哈！纪念一下……

现在总结一下递归遍历出所有摆放的问题，这类问题比如这道火力网，或者8皇后，还有以前的排球运动员问题。

 

可以写一个putCell的递归方法。

public void putCell(int row,int column){cell next=FindNext(row,column);if(canPut(row,column)){doPutAction();//在Array里标记，已经放了putCellToArrangedList();//放一个list，后面倒退方便}if(next==null){PrintCurrentArray();//一次遍历的结束}else{putCell(next.row, next.column);//这个放好了，放下一个}//到这里全部放好了，后退一步，看下一种可能if (!this.arrangedList.isEmpty()) {cell lastGun = arrangedList.pollLast();removeLastCell();next = FindNext(lastGun.row, lastGun.column);if (next != null)PutGun(next.row, next.column);}} 

 

 

而整个火力网的代码如下：

 

import java.util.LinkedList;import java.util.Scanner;public class Main {public static void main(String[] args) {LinkedList<char[][]> allArrays = new LinkedList<char[][]>();FireNet fn = new FireNet();Scanner in = new Scanner(System.in);int rowsIn = 0;while (in.hasNext()) {String s = in.next();int scope = Integer.parseInt(s);if (scope == 0) {fn.CalculateAllArray(allArrays);//fn.printAllArray(allArrays);return;} else {rowsIn = 0;char[][] array = new char[scope][scope];while (in.hasNext()) {s = in.next();for (int i = 0; i < s.length(); i++) {array[rowsIn][i] = s.charAt(i);}rowsIn++;if (rowsIn == scope)break;}allArrays.add(array);}}}}class FireNet {public void print(String s) {System.out.print(s);}public void CalculateAllArray(LinkedList<char[][]> list) {while(!list.isEmpty()){this.maxCount=0;System.out.println(this.CalculateArray(list.pop())); }}public void print(char s) {System.out.print(s);}public void printArray(char[][] array) {int scope = array.length;for (int i = 0; i < scope; i++) {for (int j = 0; j < scope; j++) {print(array[i][j]);}print("/n");}}public void printAllArray(LinkedList<char[][]> list) {while (!list.isEmpty()) {printArray(list.pop());}}private char[][] myArray;LinkedList<cell> arrangedList = new LinkedList<cell>();int maxCount = 0;public int CalculateArray(char[][] array) {this.myArray = array;PutGun(0, 0);return maxCount;}private void PutGun(int row, int column) {cell next = FindNext(row, column);if (Canput(row, column)) {this.myArray[row][column] = 'O';this.arrangedList.add(new cell(row, column));}if (next == null) {// finish and print all// fn.printArray(this.myArray);if (this.maxCount < arrangedList.size()) {this.maxCount = arrangedList.size();}} else {PutGun(next.row, next.column);}if (!this.arrangedList.isEmpty()) {cell lastGun = this.arrangedList.pollLast();this.myArray[lastGun.row][lastGun.column] = '.';next = FindNext(lastGun.row, lastGun.column);if (next != null)PutGun(next.row, next.column);}}private cell FindNext(int row, int column) {int scope = this.myArray.length;cell c = new cell(0, 0);if (column < scope - 1) {c.row = row;c.column = column + 1;return c;} else if (column == scope - 1 && row < scope - 1) {c.row = row + 1;c.column = 0;return c;}return null;}private boolean Canput(int row, int column) {if (this.myArray[row][column] == 'X') {return false;} else {boolean up = canShootFromUp(row, column);boolean down = canShootFromDown(row, column);boolean left = canShootFromLeft(row, column);boolean right = canShootFromRight(row, column);if (up || down || left || right) {return false;} else {return true;}}}private boolean canShootFromRight(int row, int column) {while (row > 0) {row--;if (this.myArray[row][column] == 'X')return false;else if (this.myArray[row][column] == 'O')return true;}return false;}private boolean canShootFromLeft(int row, int column) {while (column > 0) {column--;if (this.myArray[row][column] == 'X')return false;else if (this.myArray[row][column] == 'O')return true;}return false;}private boolean canShootFromDown(int row, int column) {while (row < this.myArray.length - 1) {row++;if (this.myArray[row][column] == 'X')return false;else if (this.myArray[row][column] == 'O')return true;}return false;}private boolean canShootFromUp(int row, int column) {while (column < this.myArray.length - 1) {column++;if (this.myArray[row][column] == 'X')return false;else if (this.myArray[row][column] == 'O')return true;}return false;}}class cell {public cell(int row, int column) {this.row = row;this.column = column;}public int row;public int column;}