枚举——POJ1753

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POJ 1753

#include<iostream>#include<bitset>#include<queue>using namespace std;queue<bitset<16>> state;//record the state of each situation bool flag[65536] = { false };<span style="white-space:pre"></span>//in case repeated searchint step[65536] ;void Initialize(){cout << "Please input a 4*4 rectangle while 'b' represents 'black' "<< "and 'w' represents 'white':\n";char c;int i = 0, j = 0;bitset<16> temp;for (i = 0; i < 4; i++){for (j = 0; j < 4; j++){cin >> c;if ('b' == c)temp.set(4 * i + j);}}state.push(temp);flag[temp.to_ulong()] = true;}bitset<16> Flip(bitset<16> piece, int i){if (i % 4 != 0)//not in the first columnpiece.reset(i - 1);if ((i + 1) % 4 != 0)//not in the fourth columnpiece.reset(i + 1);if (i > 3)//not in the first rowpiece.reset(i - 4);if (i < 12)//not in the fourth rowpiece.reset(i + 4);return piece;}bool breadFirstSearch(){while (!state.empty()){bitset<16> firstState = state.front();state.pop();//queue.pop() do not return the value of the first item!for (int i = 0; i < 16; i++){bitset<16> temp = Flip(firstState, i);if (firstState.none() || (firstState.count() == 16)){cout << step[firstState.to_ulong()];return true;}else if(!flag[temp.to_ulong()]){state.push(temp);flag[temp.to_ulong()] = true;step[temp.to_ulong()] = step[firstState.to_ulong()] + 1;}}}return false;}int main(){Initialize();if (!breadFirstSearch())cout << "Impossible!";return 0;}

最后：

1. 2^16=65536 ,如果设置的数组大小为65535,那么

输入：

bbbb

输出则是溢出的

2. bitset<> 会比^ | &方便使用

3.广度优先遍历使用队列作为基本的数据结构，深度优先算法依赖于栈（在递归中显示或隐士地使用栈）

4.做ACM..不是为了成为ACMer，只是想对数据结构和算法有一个应用实践

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