Robots on a grid(DP+bfs())
链接:http://www.bnuoj.com/bnuoj/problem_show.php?pid=25585
Current Server Time: 2013-08-27 20:42:26
Robots on a grid
None
Graph Theory
2-SAT
Articulation/Bridge/Biconnected Component
Cycles/Topological Sorting/Strongly Connected Component
Shortest Path
Bellman Ford
Dijkstra/Floyd Warshall
Euler Trail/Circuit
Heavy-Light Decomposition
Minimum Spanning Tree
Stable Marriage Problem
Trees
Directed Minimum Spanning Tree
Flow/Matching
Graph Matching
Bipartite Matching
Hopcroft–Karp Bipartite Matching
Weighted Bipartite Matching/Hungarian Algorithm
Flow
Max Flow/Min Cut
Min Cost Max Flow
DFS-like
Backtracking with Pruning/Branch and Bound
Basic Recursion
IDA* Search
Parsing/Grammar
Breadth First Search/Depth First Search
Advanced Search Techniques
Binary Search/Bisection
Ternary Search
Geometry
Basic Geometry
Computational Geometry
Convex Hull
Pick's Theorem
Game Theory
Green Hackenbush/Colon Principle/Fusion Principle
Nim
Sprague-Grundy Number
Matrix
Gaussian Elimination
Matrix Exponentiation
Data Structures
Basic Data Structures
Binary Indexed Tree
Binary Search Tree
Hashing
Orthogonal Range Search
Range Minimum Query/Lowest Common Ancestor
Segment Tree/Interval Tree
Trie Tree
Sorting
Disjoint Set
String
Aho Corasick
Knuth-Morris-Pratt
Suffix Array/Suffix Tree
Math
Basic Math
Big Integer Arithmetic
Number Theory
Chinese Remainder Theorem
Extended Euclid
Inclusion/Exclusion
Modular Arithmetic
Combinatorics
Group Theory/Burnside's lemma
Counting
Probability/Expected Value
Others
Tricky
Hardest
Unusual
Brute Force
Implementation
Constructive Algorithms
Two Pointer
Bitmask
Beginner
Discrete Logarithm/Shank's Baby-step Giant-step Algorithm
Greedy
Divide and Conquer
Dynamic Programming
Tag it!

You have recently made a grid traversing robot that can find its way from the top left corner of a grid to the bottom right corner. However, you had forgotten all your AI programming skills, so you only programmed your robot to go rightwards and downwards (that's after all where the goal is). You have placed your robot on a grid with some obstacles, and you sit and observe. However, after a while you get tired of observing it getting stuck, and ask yourself "How many paths are there from the start position to the goal position?", and "If there are none, could the robot have made it to the goal if it could walk upwards and leftwards?"
Input
On the first line is one integer, 1 <= n <= 1000. Then follows n lines, each with n characters, where each character is one of '.' and '#', where '.' is to be interpreted as a walkable tile and '#' as a non-walkable tile. There will never be a wall at s, and there will never be a wall at t.
Output
Output one line with the number of different paths starting in s and ending in t (modulo 231-1) or THE GAME IS A LIE if you cannot go from s to t going only rightwards and downwards but you can if you are allowed to go left and up as well, or INCONCEIVABLE if there simply is no path from s to t.
Sample Input
Sample Input 1
5
.....
#..#.
#..#.
...#.
..... Sample Input 2
7
......#
####...
.#.....
.#...#.
.#.....
.#..###
.#.....
Sample Output
Sample Output 1
6 Sample Output 2
THE GAME IS A LIE 尼玛,这网页有问题!!!一个图竟然有这么大!!!!!!!
MD!!卡了老子一下午!!!!
就是一道简单的搜索+动态规划:
就是用DFS()竟然会爆栈!!!!!
世界上最污秽的词语也无法表达我现在的心情!!!!!!!!
没什么可说的Runtime error(就是爆栈)
#include<iostream>
#include<string.h>
#include<algorithm>
#include<stdio.h>
#include<math.h>
#include<queue>
using namespace std;
int flag,n;
int c1[][]={,,-,,,,,-};
long long dp[][];
const long long sb=;
char a[][];
void bfs(int x,int y)
{
int c[][];
int i,x1,y1,x2,y2;
queue<int> Q;
memset(c,,sizeof(c));
c[x][x]=;
while(!Q.empty()) Q.pop();
Q.push(x);
Q.push(y);
while(!Q.empty())
{
x1=Q.front();
Q.pop();
y1=Q.front();
Q.pop();
if(x1==n-&&y1==n-)
{
flag=;
return ;
}
if(flag)
return ;
for(i=;i<;i++)
{
x2=x1+c1[i][];
y2=y1+c1[i][];
if(x2>=&&x2<n&&y2>=&&y2<n&&a[x2][y2]!='#'&&!c[x2][y2])
{
c[x2][y2]=;
Q.push(x2);
Q.push(y2);
}
}
}
}
int main()
{
int i,j;
while(scanf("%d",&n)!=EOF)
{
for(i=;i<n;i++)
scanf("%s",a[i]);
memset(dp,,sizeof(dp));
dp[][]=;
for(i=;i<n;i++)
for(j=;j<n;j++)
if(a[i][j]!='#')
{
if(i->=&&a[i-][j]!='#')
dp[i][j]+=dp[i-][j];
if(j->=&&a[i][j-]!='#')
dp[i][j]+=dp[i][j-];
dp[i][j]%=sb;
}
if(dp[n-][n-]==)
{
flag=;
bfs(,);
if(flag)
printf("THE GAME IS A LIE\n");
else
printf("INCONCEIVABLE\n");
}
else
printf("%lld\n",dp[n-][n-]);
}
return ;
}
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