Solve #303

Author: aylei

src/lib.rs

@@ -225,3 +225,4 @@ mod n0295_find_median_from_data_stream;
 mod n0299_bulls_and_cows;
 mod n0300_longest_increasing_subsequence;
 mod n0301_remove_invalid_parentheses;
+mod n0303_range_sum_query_immutable;

src/n0303_range_sum_query_immutable.rs

@@ -0,0 +1,71 @@
+/**
+ * [303] Range Sum Query - Immutable
+ *
+ * Given an integer array nums, find the sum of the elements between indices i and j (i ≤ j), inclusive.
+ *
+ * Example:<br>
+ *
+ * Given nums = [-2, 0, 3, -5, 2, -1]
+ *
+ * sumRange(0, 2) -> 1
+ * sumRange(2, 5) -> -1
+ * sumRange(0, 5) -> -3
+ *
+ *
+ *
+ * Note:<br>
+ * <ol>
+ * You may assume that the array does not change.
+ * There are many calls to sumRange function.
+ * </ol>
+ *
+ */
+pub struct Solution {}
+
+// submission codes start here
+
+struct NumArray {
+    nums: Vec<i32>,
+}
+
+/**
+ * `&self` means the method takes an immutable reference.
+ * If you need a mutable reference, change it to `&mut self` instead.
+ */
+impl NumArray {
+    fn new(nums: Vec<i32>) -> Self {
+        let mut res = 0;
+        let mut vec = Vec::with_capacity(nums.len());
+        for &num in nums.iter() {
+            res += num;
+            vec.push(res);
+        }
+        NumArray{nums: vec}
+    }
+
+    fn sum_range(&self, i: i32, j: i32) -> i32 {
+        let (i, j) = (i as usize, j as usize);
+        self.nums[j] - if i > 0 { self.nums[i-1] } else { 0 }
+    }
+}
+
+/**
+ * Your NumArray object will be instantiated and called as such:
+ * let obj = NumArray::new(nums);
+ * let ret_1: i32 = obj.sum_range(i, j);
+ */
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_303() {
+        let mut nums = NumArray::new(vec![-2, 0, 3, -5, 2, -1]);
+        assert_eq!(nums.sum_range(0, 2), 1);
+        assert_eq!(nums.sum_range(2, 5), -1);
+        assert_eq!(nums.sum_range(0, 5), -3);
+    }
+}