Word Wrap Problem

AlgorithmsData StructureDynamic Programming

A sequence of words is given, there is a limit on the number of characters for each line. By putting line breaks, in such a way that lines are printed clearly.

The lines must be balanced, when some lines have lots of extra spaces and some lines are containing a small number of extra spaces, it will balance them to separate lines. It tries to use the same number of extra spaces to make them balanced.

This algorithm will produce how many words can be placed in one line, and how many lines are needed.

Input and Output

Input:
The length of words for each line. {3, 2, 2, 5}. The max width is 6.
Output:
Line number 1: Word Number: 1 to 1 (only one word)
Line number 2: Word Number: 2 to 3 (Second and 3rd word)
Line number 3: Word Number: 4 to 4 (4th word)

Algorithm

wordWrap(wordLenArr, size, maxWidth)

Input − The word length array, size of the array and the maximum width of the word.

Output − List of how many words will place per line.

Begin
   define two square matrix extraSpace and lineCost of order (size + 1)
   define two array totalCost and solution of size (size + 1)

   for i := 1 to size, do
      extraSpace[i, i] := maxWidth – wordLenArr[i - 1]
      for j := i+1 to size, do
         extraSpace[i, j] := extraSpace[i, j-1] – wordLenArr[j - 1] - 1
      done
   done

   for i := 1 to size, do
      for j := i+1 to size, do
         if extraSpace[i, j] < 0, then
            lineCost[i, j] = ∞
         else if j = size and extraSpace[i, j] >= 0, then
            lineCost[i, j] := 0
         else
            linCost[i, j] := extraSpace[i, j]^2
      done
   done

   totalCost[0] := 0
   for j := 1 to size, do
      totalCost[j] := ∞
      for i := 1 to j, do
         if totalCost[i-1] ≠∞ and linCost[i, j] ≠ ∞ and
            (totalCost[i-1] + lineCost[i,j] < totalCost[j]), then
            totalCost[i – 1] := totalCost[i – 1] + lineCost[i, j]
            solution[j] := i
      done
   done
   display the solution matrix
End

Example

#include<iostream>
using namespace std;

int dispSolution (int solution[], int size) {
   int k;
   if (solution[size] == 1)
      k = 1;
   else
      k = dispSolution (solution, solution[size]-1) + 1;
   cout << "Line number "<< k << ": Word Number: " <<solution[size]<<" to "<< size << endl;
   return k;
}

void wordWrap(int wordLenArr[], int size, int maxWidth) {
   int extraSpace[size+1][size+1];
   int lineCost[size+1][size+1];
   int totalCost[size+1];
   int solution[size+1];

   for(int i = 1; i<=size; i++) {    //find extra space for all lines
      extraSpace[i][i] = maxWidth - wordLenArr[i-1];

      for(int j = i+1; j<=size; j++) {    //extra space when word i to j are in single line
         extraSpace[i][j] = extraSpace[i][j-1] - wordLenArr[j-1] - 1;
      }
   }

   for (int i = 1; i <= size; i++) {    //find line cost for previously created extra spaces array

      for (int j = i; j <= size; j++) {

         if (extraSpace[i][j] < 0)
            lineCost[i][j] = INT_MAX;
         else if (j == size && extraSpace[i][j] >= 0)
            lineCost[i][j] = 0;
         else
            lineCost[i][j] = extraSpace[i][j]*extraSpace[i][j];
      }
   }

   totalCost[0] = 0;
   for (int j = 1; j <= size; j++) {    //find minimum cost for words
      totalCost[j] = INT_MAX;

      for (int i = 1; i <= j; i++) {
         if (totalCost[i-1] != INT_MAX && lineCost[i][j] != INT_MAX && (totalCost[i-1] + lineCost[i][j] < totalCost[j])){
            totalCost[j] = totalCost[i-1] + lineCost[i][j];
            solution[j] = i;
         }
      }
   }

   dispSolution(solution, size);
}

main() {
   int wordLenArr[] = {3, 2, 2, 5};
   int n = 4;
   int maxWidth = 6;
   wordWrap (wordLenArr, n, maxWidth);
}

Output

Line number 1: Word Number: 1 to 1
Line number 2: Word Number: 2 to 3
Line number 3: Word Number: 4 to 4
raja
Published on 11-Jul-2018 16:16:29
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