# Color a grid such that all same color cells are connected either horizontally or vertically

• Last Updated : 26 Jul, 2021

Given three integers R, C, N, and an array arr[] of size N. The task is to color all cells of a grid of R rows and C columns such that all same color cells are connected either horizontally or vertically. N represents the colors numbered from 1 to N and arr[] denotes the quantity of each color. The total quantity of color is exactly equal to the total number of cells of the grid.
Approach:

Input: R = 3, C = 5, N = 5, arr[] = {1, 2, 3, 4, 5}
Output:
1 4 4 4 3
2 5 4 5 3
2 5 5 5 3
Explanation: Available colors are 1(count = 1), 2(count = 2), 3(count = 3) etc.
For color 5: we can reach all color 5s by going horizontally or vertically through the same color 5.
Similarly for color 3, the rightmost row contains all 3 etc.
Similarly, for the rest of the colors 1, 2, 4.
Below is an invalid grid:
1 4 3 4 4
2 5 4 5 3
2 5 5 5 3
This is because the connection for the colors 3 and 4 has been broken by the invalid position of 3
in the position(0, 2).We can no longer traverse through all the 4s or all the 3s, horizontally or vertically, by passing through the respective 3s and 4s only.
Input: R = 2, C = 2, N = 3, arr[] = {2, 1, 1}
Output:
1 1
2 3

Approach:

At first glance, it might seem that graph algorithms are required. However, we are going to follow an optimized greedy algorithm

1. Create a new 2D array which will be our final grid. Let us call it dp[][].
2. Traverse the color array A[]
3. For each color, i having A[i] quantities
• If the row is an odd-numbered row, fill the dp array from left to right
• Else if it is an even row, fill it from right to left
4. If the quantity of color is used up, move on to the next color greedily

Below is the implementation of the above approach:

## C++

 `// C++ Program to Color a grid``// such that all same color cells``// are connected either``// horizontally or vertically` `#include ``using` `namespace` `std;` `void` `solve(vector<``int``>& arr,``        ``int` `r, ``int` `c)``{``    ``// Current color``    ``int` `idx = 1;` `    ``// final grid``    ``int` `dp[r];` `    ``for` `(``int` `i = 0; i < r; i++) {` `        ``// if even row``        ``if` `(i % 2 == 0) {` `            ``// traverse from left to``            ``// right``            ``for` `(``int` `j = 0; j < c; j++) {` `                ``// if color has been exhausted``                ``//, move to the next color``                ``if` `(arr[idx - 1] == 0)``                    ``idx++;` `                ``// color the grid at``                ``// this position``                ``dp[i][j] = idx;` `                ``// reduce the color count``                ``arr[idx - 1]--;``            ``}``        ``}``        ``else` `{` `            ``// traverse from right to``            ``// left for odd rows``            ``for` `(``int` `j = c - 1; j >= 0; j--) {``                ``if` `(arr[idx - 1] == 0)``                    ``idx++;``                ``dp[i][j] = idx;``                ``arr[idx - 1]--;``            ``}``        ``}``    ``}` `    ``// print the grid``    ``for` `(``int` `i = 0; i < r; ++i) {``        ``for` `(``int` `j = 0; j < c; ++j) {``            ``cout << dp[i][j] << ``" "``;``        ``}``        ``cout << endl;``    ``}``}` `// Driver code``int` `main()``{``    ``int` `r = 3, c = 5;``    ``int` `n = 5;``    ``vector<``int``> arr``        ``= { 1, 2, 3, 4, 5 };``    ``solve(arr, r, c);``    ``return` `0;``}`

## Java

 `// Java program to color a grid       ``// such that all same color cells       ``// are connected either       ``// horizontally or vertically       ``import` `java.util.*;   ` `class` `GFG{       ``            ` `static` `void` `solve(List arr,``                ``int` `r, ``int` `c)       ``{``    ` `    ``// Current color       ``    ``int` `idx = ``1``;       ``            ` `    ``// Final grid       ``    ``int``[][] dp = ``new` `int``[r];       ``            ` `    ``for``(``int` `i = ``0``; i < r; i++)``    ``{       ``        ` `        ``// If even row       ``        ``if` `(i % ``2` `== ``0``)``        ``{``            ` `            ``// Traverse from left to       ``            ``// right       ``            ``for``(``int` `j = ``0``; j < c; j++)``            ``{``                ` `                ``// If color has been exhausted``                ``//, move to the next color``                ``if` `(arr.get(idx - ``1``) == ``0``)   ``                    ``idx++;``                ` `                ``// Color the grid at``                ``// this position``                ``dp[i][j] = idx;``                ` `                ``// Reduce the color count``                ``arr.set(idx - ``1``,``                ``arr.get(idx - ``1``) - ``1``);``            ``}``        ``}``        ``else``        ``{``            ` `            ``// Traverse from right to``            ``// left for odd rows``            ``for``(``int` `j = c - ``1``; j >= ``0``; j--)``            ``{``                ``if` `(arr.get(idx - ``1``) == ``0``)   ``                    ``idx++;``            ` `                ``dp[i][j] = idx;``            ` `                ``arr.set(idx - ``1``,``                ``arr.get(idx - ``1``) - ``1``);``            ``}       ``        ``}       ``    ``}       ``            ` `    ``// Print the grid       ``    ``for``(``int` `i = ``0``; i < r; ++i)``    ``{       ``        ``for``(``int` `j = ``0``; j < c; ++j)``        ``{       ``            ``System.out.print(dp[i][j] + ``" "``);       ``        ``}       ``        ``System.out.println();       ``    ``}       ``}       ``        ` `// Driver Code       ``public` `static` `void` `main (String[] args)``{       ``    ``int` `r = ``3``, c = ``5``;       ``    ``int` `n = ``5``;       ``    ``List arr = Arrays.asList(``1``, ``2``, ``3``, ``4``, ``5``);``    ` `    ``solve(arr, r, c);       ``}       ``}` `// This code is contributed by offbeat`

## Python3

 `# Python3 program to color a grid``# such that all same color cells``# are connected either``# horizontally or vertically``def` `solve(arr, r, c):``    ` `    ``# Current color``    ``idx ``=` `1` `    ``# Final grid``    ``dp ``=` `[[``0` `for` `i ``in` `range``(c)]``            ``for` `i ``in` `range``(r)]` `    ``for` `i ``in` `range``(r):` `        ``# If even row``        ``if` `(i ``%` `2` `=``=` `0``):` `            ``# Traverse from left to``            ``# right``            ``for` `j ``in` `range``(c):` `                ``# If color has been exhausted,``                ``# move to the next color``                ``if` `(arr[idx ``-` `1``] ``=``=` `0``):``                    ``idx ``+``=` `1` `                ``# Color the grid at``                ``# this position``                ``# print(i,j)``                ``dp[i][j] ``=` `idx` `                ``# Reduce the color count``                ``arr[idx ``-` `1``] ``-``=` `1``        ``else``:` `            ``# Traverse from right to``            ``# left for odd rows``            ``for` `j ``in` `range``(c ``-` `1``, ``-``1``, ``-``1``):``                ``if` `(arr[idx ``-` `1``] ``=``=` `0``):``                    ``idx ``+``=` `1``                    ` `                ``dp[i][j] ``=` `idx``                ``arr[idx ``-` `1``] ``-``=` `1` `    ``# Print the grid``    ``for` `i ``in` `range``(r):``        ``for` `j ``in` `range``(c):``            ``print``(dp[i][j], end ``=` `" "``)` `        ``print``()` `# Driver code``if` `__name__ ``=``=` `'__main__'``:` `    ``r ``=` `3``    ``c ``=` `5``    ``n ``=` `5``    ``arr ``=` `[ ``1``, ``2``, ``3``, ``4``, ``5` `]``    ` `    ``solve(arr, r, c)` `# This code is contributed by mohit kumar 29`

## C#

 `// C# program to color a grid       ``// such that all same color cells       ``// are connected either       ``// horizontally or vertically       ``using` `System;``using` `System.Collections.Generic;` `class` `GFG{       ``            ` `static` `void` `solve(List<``int``> arr,``                ``int` `r, ``int` `c)       ``{``    ` `    ``// Current color       ``    ``int` `idx = 1;       ``            ` `    ``// Final grid       ``    ``int``[,] dp = ``new` `int``[r, c];       ``            ` `    ``for``(``int` `i = 0; i < r; i++)``    ``{       ``        ` `        ``// If even row       ``        ``if` `(i % 2 == 0)``        ``{``            ` `            ``// Traverse from left to       ``            ``// right       ``            ``for``(``int` `j = 0; j < c; j++)``            ``{``                ` `                ``// If color has been exhausted,``                ``// move to the next color``                ``if` `(arr[idx - 1] == 0)   ``                    ``idx++;``                ` `                ``// Color the grid at``                ``// this position``                ``dp[i, j] = idx;``                ` `                ``// Reduce the color count``                ``arr[idx - 1] = arr[idx - 1] - 1;``            ``}``        ``}``        ``else``        ``{``            ` `            ``// Traverse from right to``            ``// left for odd rows``            ``for``(``int` `j = c - 1; j >= 0; j--)``            ``{``                ``if` `(arr[idx - 1] == 0)   ``                    ``idx++;``            ` `                ``dp[i, j] = idx;``                ``arr[idx - 1] = arr[idx - 1] - 1;``            ``}       ``        ``}       ``    ``}       ``            ` `    ``// Print the grid       ``    ``for``(``int` `i = 0; i < r; ++i)``    ``{       ``        ``for``(``int` `j = 0; j < c; ++j)``        ``{       ``            ``Console.Write(dp[i, j] + ``" "``);       ``        ``}       ``        ``Console.Write(``'\n'``);       ``    ``}       ``}       ``        ` `// Driver Code       ``public` `static` `void` `Main (``string``[] args)``{       ``    ``int` `r = 3, c = 5;       ``    ``//int n = 5;   ``    ` `    ``List<``int``> arr = ``new` `List<``int``>();``    ``arr.Add(1);``    ``arr.Add(2);``    ``arr.Add(3);``    ``arr.Add(4);``    ``arr.Add(5);``    ` `    ``solve(arr, r, c);       ``}       ``}` `// This code is contributed by rutvik_56`

## Javascript

 ``

Output:

```1 2 2 3 3
4 4 4 4 3
5 5 5 5 5```

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