SRM 582 Div II Level Three： ColorTheCells, Brute Force 算法

题目来源：http://community.topcoder.com/stat?c=problem_statement&pm=12581

Burte Force 算法，求解了所有了情况，注意 next_permutation 函数的用法。

#include <iostream>#include <vector>#include <limits>#include <algorithm>using namespace std;class ColorTheCells{private:vector <int> dryingTime;/* 需要干燥的时间  */vector <long> dryedTime;/* 正好干燥的时间，0表示还没有paint */vector <int> paint_order;/* paint格子的顺序 */public:long calc(int seq);int minimalTime(vector <int> dryingTime);};#define MOVE_TIME 1L#define PAINT_TIME 1L#define INFINITY_TIME LONG_MAX /* 参考Ueddy代码实现 */int ColorTheCells::minimalTime(vector<int> dryingTime){int num = dryingTime.size();long minTime = INFINITY_TIME;int i, j;this->dryingTime = dryingTime;paint_order.clear();/* paint 的顺序 */dryedTime.clear();for (i = 0; i < num; i++) {paint_order.push_back(i);dryedTime.push_back(0);}/* brute force，枚举所有的情况，选出最小时间 */do {for (i = 0; i < (1<<num); i++) {for (j = 0; j < num; j++) {dryedTime[j] = 0;}minTime = min(minTime, calc(i));}} while (next_permutation(paint_order.begin(), paint_order.end()));return minTime;}/** * seq为一个序列，0表示在被paint位置左边paint, 1表示在右边paint，paint的顺序由 * paint_order指定。 */long ColorTheCells::calc(int seq){long time;/* 所用时间 */int num = dryingTime.size();int paint_dir;/* paint方向，在被paint位置左边还是右边paint */int cur_pos;/* 当前位置 */int paint_pos;/* paint位置，不是被paint的位置 */int bias;/* 从当前位置向左走还是向右走 */cur_pos = 0;time = 0;for (int i = 0; i < num; i++) {paint_dir = seq & 1;seq /= 2;paint_dir = paint_dir ? 1 : -1;paint_pos = paint_order[i] + paint_dir;if (paint_pos < 0 || paint_pos >= num) {/* 位置不合法 */return INFINITY_TIME;}bias = 1;/* 从当前位置向右走 */if (cur_pos - paint_pos > 0) {/* 从当前位置向左走 */bias = -1;}/* 用for循环到达paint位置，中间遇到还没有干燥的格子要等待 */for (; cur_pos != paint_pos; cur_pos += bias) {if (dryedTime[cur_pos+bias] > time) {/* 等待干燥 */time = dryedTime[cur_pos+bias];}time += MOVE_TIME;/* 移动时间 */}time += PAINT_TIME;/* 到达目的地，paint时间 */dryedTime[paint_order[i]] = time + dryingTime[paint_order[i]];/* 更新该格子干燥时间  */}return time;}