"One Day together Leetcode" #85. Maximal Rectangle

One Day together Leetcode

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(i) Title

Given a 2D binary matrix filled with 0 's and 1 ' s, find the largest rectangle containing all ones and return to its area.

(ii) Problem solving

Topic: Given a binary matrix, the maximum area of all sub-matrices containing 1 is calculated in the matrix.
For example:
1000
1101
1111
1111
The formed rectangle has a No. 0 column area of 4, 2nd, 3 row area 8 and so on.
So let's think about how to find these rectangles and figure out their area.
for (I,J) we have it as the upper left corner of the rectangle, then need to find out how many 1 it extends to the right, how many 1 it extends down, and how many 1 of each line extends to the right, such as (1,0) extends right 2 1, down 3 1, then (2,0), (3,0) to the right extends greater than 2, So the area of this rectangle is 6.

classSolution { Public:intMaximalrectangle ( vector<vector<char>>& Matrix) {if(Matrix.empty ())return 0;introw = Matrix.size ();intCol = matrix[0].size (); vector<vector<int>>Samerownum;//Store The current point down how many 1         vector<vector<int>>Samecolnum;//Store current point extend to right how many 1         for(inti =0; i < row; i++) { vector<int>TMP (COL,0);            Samecolnum.push_back (TMP);        Samerownum.push_back (TMP); } for(inti =0; i < row; i++)//Calculation Samerownum{ for(intj =0; J < Col; )            {if(Matrix[i][j] = =' 1 ') {intt = j;intCount =0; while(T < col&&matrix[i][t++] = =' 1 ') count++;//calculation of how many 1                     while(j<t) samecolnum[i][j++] = count--;//Assigned value}Elsej + +; }        } for(inti =0; I < col; i++) { for(intj =0; J < Row; )            {if(Matrix[j][i] = =' 1 ') {intt = j;intCount =0; while(T < row&&matrix[t++][i] = =' 1 ') count++;//calculation of how many 1                     while(j<t) Samerownum[j++][i] = count--;//Assigned value}Elsej + +; }        }intMaxarea =0; for(inti =0; i < row; i++) { for(intj =0; J < col;j++) {if(matrix[i][j]==' 1 ')                {intt = i;intMincol = Samecolnum[i][j]; while(T < row&&t < i + samerownum[i][j]) {Mincol = Mincol < Samecolnum[t][j]? Mincol:samecolnum[t][j];//Calculate the rectangular area in turn                        intArea = mincol* (t-i+1); Maxarea = max (Maxarea, area);//Seek maximum valuet++; }                }            }        }returnMaxarea; }};

"One Day together Leetcode" #85. Maximal Rectangle