20240419 Finished

src/problem/mod.rs

@@ -105,4 +105,5 @@ mod p274_h_index;
 mod p380_insert_delete_getrandom_o1;
 mod p238_product_of_array_except_self;
 mod p134_gas_station;
-mod p135_candy;
+mod p135_candy;
+mod p42_trapping_rain_water;

src/problem/p42_trapping_rain_water.rs

@@ -0,0 +1,42 @@
+/**
+ * [42] Trapping Rain Water
+ */
+pub struct Solution {}
+
+// submission codes start here
+
+impl Solution {
+    pub fn trap(height: Vec<i32>) -> i32 {
+        let length = height.len();
+        let mut left_max = vec![height[0]; length];
+        let mut right_max = vec![height[length - 1]; length];
+
+        for i in (1..length) {
+            left_max[i] = left_max[i - 1].max(height[i]);
+        }
+
+        for i in (0..length - 1).rev() {
+            right_max[i] = right_max[i + 1].max(height[i]);
+        }
+
+        let mut result = 0;
+
+        for i in 0..length {
+            result += left_max[i].min(right_max[i]) - height[i];
+        }
+
+        result
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_42() {
+        assert_eq!(6, Solution::trap(vec![0, 1, 0, 2, 1, 0, 1, 3, 2, 1, 2, 1]));
+    }
+}