upd

Author: brebenelmihnea

solutions/gold/cses-1148

@@ -9,15 +9,15 @@ prerequisites:
 
 ## Explanation
 
-Precompute $r_{i,j}$ as the number of continuous free cells starting from $(i, j)$ ending at $(i, j + r_{i, j})$, 
-Similarly to [Maximum Buildin I](https://cses.fi/problemset/task/1147) apply monotonic stacks to find:
+Precompute $r_{i,j}$ as the maximum number of continuous free cells on line $i$ starting from $(i, j)$ to the right.
+Similarly to [Maximum Building I](https://cses.fi/problemset/task/1147) apply monotonic stacks to find:
 - $u_{i, j}$ , the last line above $i$ with cell $(x, j)$ such that $r_{x, j} > r_{i, j}$
 - $d_{i, j}$ , the last line under $i$ with cell $(y, j)$ such that $r_{y, j} \ge r_{i, j}$
 
-Using [prefix sums](/silver/more-prefix-sums#2d-prefix-sums) and [difference arrays](https://medium.com/@ishankkatiyar162/understanding-difference-array-the-underrated-constant-time-range-update-algorithm-part-1-e432ada7f1f5) we can effitiently update the answer matrix. 
-Having $r_{i,j}$, $u_{i,j}$ and $d_{i,j}$ precomputed, we know the upperbound and the lowerbound of the rectangle
-of of width $r_{i,j}$ i.e. how much it can expand up above and below line $i$ maintaing width $r_{i, j}$. 
-We'll do difference arrays on each column independently. Therefore, the updates of the answer matrix look like this:
+Using [prefix sums](/silver/more-prefix-sums#2d-prefix-sums) and [difference arrays](https://codeforces.com/blog/entry/78762) 
+we can efficiently update the answer matrix. Having $r_{i,j}$, $u_{i,j}$ and $d_{i,j}$ precomputed, we know the upperbound 
+and the lowerbound of the rectangle of of width $r_{i,j}$ i.e. how much it can expand above and below line $i$ maintaing width $r_{i, j}$. 
+We'll do difference arrays on each column independently. Accordingly, the updates of the answer matrix look like this:
 - $ans[1][r_{i,j}]++$
 - $ans[i - u_{i, j} + 2][r_{i,j}]--$ , the upperbound
 - $ans[d_{i,j} - i + 2][r_{i, j}]]--$ , the lowerbound