[feat ]: leetcode 85

Signed-off-by: Bo-Wei Chen(BWbwchen) <tim.chenbw@gmail.com>

Author: BWbwchen

leetcode/85.cpp renamed to leetcode/0085_Maximal-Rectangle.cpp

@@ -0,0 +1,48 @@
+use std::cmp::max;
+impl Solution {
+    pub fn maximal_rectangle(matrix: Vec<Vec<char>>) -> i32 {
+        let mut histagram = vec![0; matrix.get(0).unwrap().len()];
+        let mut ret = 0;
+
+        for (i, row) in matrix.iter().enumerate() {
+            // build histagram that begin from the first row and end at this row.
+            for (j, v) in row.iter().enumerate() {
+                if *v == '0' {
+                    histagram[j] = 0;
+                } else {
+                    histagram[j] += 1;
+                }
+            }
+            ret = max(ret, Self::get_area(&matrix, &mut histagram));
+        }
+        ret
+    }
+    fn get_area(matrix: &Vec<Vec<char>>, hist: &mut Vec<i32>) -> i32 {
+        // monotonic stack with the biggest top value.
+        let mut mst: Vec<(i32, i32)> = Vec::new();
+        let mut ret = 0;
+
+        hist.push(0);
+
+        for (col, height) in hist.iter().enumerate() {
+            while !mst.is_empty() && (mst.last().unwrap().1 > *height) {
+                // value `height` smaller than the top, calculate the temp ans
+                
+                // the area is:
+                // height = the height of the top element of the stack
+                // width = (idx right now - 1) - the second biggest element idx.
+                let prev = mst.last().unwrap_or(&(-1, 0)).clone();
+                mst.pop();
+                let prev_height = prev.1;
+                let prev_width = col as i32 - mst.last().unwrap_or(&(-1, 0)).0 - 1;
+                let tmp_area = prev_height * prev_width;
+                ret = max(ret, tmp_area)
+            }
+            mst.push((col as i32, *height));
+        }
+
+        hist.pop();
+
+        ret
+    }
+}