solve: 42. Trapping Rain Water in rustlang

Signed-off-by: rajput-hemant <rajput.hemant2001@gmail.com>

Author: rajput-hemant

src/0001-0100/042 - Trapping Rain Water/trapping_rain_water.rs

@@ -0,0 +1,34 @@
+impl Solution {
+    pub fn trap(height: Vec<i32>) -> i32 {
+        let (mut left, mut right) = (0, height.len() - 1);
+        let (mut left_max, mut right_max) = (0, 0);
+        let mut ans = 0;
+
+        // iterate from both sides to the middle
+        while left < right {
+            // if left is lower than right, then the water level depends on left
+            // else the water level depends on right
+            if height[left] < height[right] {
+                // if left height is higher than left_max, then update left_max
+                // else add the difference between left_max and left height to ans
+                if height[left] >= left_max {
+                    left_max = height[left];
+                } else {
+                    ans += left_max - height[left];
+                }
+                left += 1;
+            } else {
+                // if right height is higher than right_max, then update right_max
+                // else add the difference between right_max and right height to ans
+                if height[right] >= right_max {
+                    right_max = height[right];
+                } else {
+                    ans += right_max - height[right];
+                }
+                right -= 1;
+            }
+        }
+
+        ans
+    }
+}