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; }