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childPoliceDistance.cpp
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childPoliceDistance.cpp
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//
// Created by Ally Wang on 25/04/15.
//
// Find all the distance from child (0) to the closest police(1), but cannot get across the wall(2)
// Mind visited to mark visited node.
//
#include <iostream>
#include <vector>
#include <queue>
#include <utility> // make_pair and pair
using namespace std;
void bfs(int row, int col, int M, int N, vector<vector<int>> grid, vector<vector<int>> &res)
{
vector<vector<bool>> visited(M, vector<bool>(N, false));
// keyword to mark the repeated node
queue<pair<int, int>> po;
po.push(make_pair(row,col));
po.push(make_pair(-5,-5)); // mark the boundary
int dist = 0;
while(!po.empty())
{
pair<int, int> p = po.front();
po.pop();
int i = p.first;
int j = p.second;
//cout << i << " " << j << endl;
if(i == -5)
{
if(po.empty()) break;
dist++;
po.push(make_pair(-5,-5));
}
else{
if( i < 0 || i >= M || j < 0 || j >= N) continue;
if(visited[i][j]) continue; // !! avoid repeated node pushed in
visited[i][j] = true;
if(grid[i][j] == 2) continue;
if(grid[i][j] == 1)
{
res[i][j] = 0;
}
else
{
if(res[i][j] == -1)
{
res[i][j] = dist;
}else{
res[i][j] = min(dist, res[i][j]);
}
}
po.push(make_pair(i-1, j));
po.push(make_pair(i+1, j));
po.push(make_pair(i, j-1));
po.push(make_pair(i, j+1));
}
}
}
vector<vector<int>> smallestDistance(vector<vector<int>> &grid) {
//if(grid.size() <= 0 || grid[0].size() <= 0) return 0;
int M = grid.size();
int N = grid[0].size();
vector<vector<int>> res(M, vector<int>(N, -1));
for(int i = 0; i < M; ++i)
{
for(int j = 0; j < N; ++j)
{
if(grid[i][j] == 1)
bfs(i, j, M, N, grid, res);
}
}
return res;
}
void vectorDisplay(vector<vector<int>> grid)
{
int M = grid.size();
int N = grid[0].size();
for(int i = 0; i < M; ++i)
{
for(int j = 0; j < N; ++j)
{
cout << grid[i][j]<< " ";
}
cout << endl;
}
return;
}
int main() {
vector<vector<int>> grid(3, vector<int> (3, 0));
grid = {
{0, 1, 0},
{0, 2, 0},
{0, 0, 0}
};
cout << "grid: " << endl;
vectorDisplay(grid);
vector<vector<int>> outp(3, vector<int> (3, 0));
outp = smallestDistance(grid);
cout << "the smallest distance from child(0) to police(1): "<<endl;
vectorDisplay(outp);
cout << endl;
grid = {
{0, 2, 0},
{0, 2, 0},
{0, 2, 1}
};
cout << "grid: " <<endl;
vectorDisplay(grid);
outp = smallestDistance(grid);
cout << "the smallest distance from child(0) to police(1): "<<endl;
vectorDisplay(outp);
cout <<endl;
return 0;
}