java - Array index out of bounds - 2d to 1d -

i working algs4 8-puzzle program presented princeton. getting array index out of bounds exception in second loop. see issue throwing exception? board class + relevant method looks this:

public class board {  private final int[][] blocks;  private final int n;   // construct board n-by-n array of blocks  // (where blocks[i][j] = block in row i, column j)     public board(int[][] blocks){      n = blocks.length;      this.blocks = new int[n][];      (int i=0; i<n; i++){       this.blocks[i] = arrays.copyof(blocks[i], n);      }     }      // board dimension n     public int dimension(){      return this.n;     }     //is board solvable?     public boolean issolvable(){       int inversions = 0;        list<integer> convert = new arraylist<>(); // convert 2d 1d        (int = 0; < blocks.length; i++){           (int j = 0; j < blocks[i].length; j++){               convert.add(blocks[i][j]);           }       }       (int = 0; < blocks.length; i++){ //counts number of inversions            if (convert.get(i) < convert.get(i-1)){ //arrayindexoutofbounds -1               inversions++;            }       }       if (inversions % 2 == 0){           return true; //even        }       return false; //odd    } 

convert.get(i-1) out of bounds when i==0.

you should change start index of loop :

  (int = 1; < blocks.length; i++){ //counts number of inversions        if (convert.get(i) < convert.get(i-1)){            inversions++;        }   }