Solve #307

Author: aylei

src/lib.rs

@@ -229,3 +229,4 @@ mod n0303_range_sum_query_immutable;
 mod n0304_range_sum_query_2d_immutable;
 mod n1009_pancake_sorting;
 mod n0306_additive_number;
+mod n0307_range_sum_query_mutable;

src/n0307_range_sum_query_mutable.rs

@@ -0,0 +1,134 @@
+/**
+ * [307] Range Sum Query - Mutable
+ *
+ * Given an integer array nums, find the sum of the elements between indices i and j (i ≤ j), inclusive.
+ *
+ * The update(i, val) function modifies nums by updating the element at index i to val.
+ *
+ * Example:
+ *
+ *
+ * Given nums = [1, 3, 5]
+ *
+ * sumRange(0, 2) -> 9
+ * update(1, 2)
+ * sumRange(0, 2) -> 8
+ *
+ *
+ * Note:
+ *
+ * <ol>
+ * 	The array is only modifiable by the update function.
+ * 	You may assume the number of calls to update and sumRange function is distributed evenly.
+ * </ol>
+ *
+ */
+pub struct Solution {}
+
+// Segement Tree
+//
+//                       N[0:6]
+//                  /               \
+//                 /                 \
+//           N[0:3]                   N[4:6]
+//         /        \               /        \
+//     N[0:1]       N[2:3]      N[4:5]      N[6]
+//    /    \        /    \     /     \
+//   N[0]  N[1]   N[2]  N[3]  N[4]  N[5]
+//
+// submission codes start here
+
+struct NumArray {
+    tree: Vec<i32>,
+    n: usize,
+}
+
+/**
+ * `&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 n = nums.len();
+        let mut tree = vec![0; 4*n];
+        if n > 0 {
+            NumArray::build(1, 0, n-1, &mut tree, &nums);
+        }
+        NumArray{tree: tree, n: n}
+    }
+
+    fn update(&mut self, i: i32, val: i32) {
+        NumArray::update_internal(i as usize, val, 1, 0, self.n-1, &mut self.tree);
+    }
+
+    fn sum_range(&self, i: i32, j: i32) -> i32 {
+        NumArray::sum(1, 0, self.n-1, i as usize, j as usize, &self.tree)
+    }
+
+    fn build(node: usize, start: usize, end: usize, tree: &mut Vec<i32>, nums: &Vec<i32>) {
+        if start == end {
+            tree[node] = nums[start];
+        } else {
+            let mid = (start + end) / 2;
+            NumArray::build(2*node, start, mid, tree, nums);
+            NumArray::build(2*node+1, mid+1, end, tree, nums);
+            tree[node] = tree[2*node] + tree[2*node+1];
+        }
+    }
+
+    fn update_internal(i: usize, val: i32, node: usize, start: usize, end: usize, tree: &mut Vec<i32>) {
+        if start == end {
+            tree[node] = val;
+        } else {
+            let mid = (start + end) / 2;
+            if i <= mid {
+                NumArray::update_internal(i, val, 2*node, start, mid, tree);
+            } else {
+                NumArray::update_internal(i, val, 2*node+1, mid+1, end, tree);
+            }
+            tree[node] = tree[2*node] + tree[2*node+1];
+        }
+    }
+
+    fn sum(node: usize, start: usize, end: usize, left: usize, right: usize, tree: &Vec<i32>) -> i32 {
+        if right < start || left > end {
+            // not in range
+            0
+        } else if left <= start && end <= right {
+            // completely in range
+            tree[node]
+        } else {
+            // partially in range
+            let mid = (start + end) / 2;
+            NumArray::sum(2*node, start, mid, left, right, tree) +
+                NumArray::sum(2*node+1, mid+1, end, left, right ,tree)
+        }
+    }
+}
+
+/**
+ * Your NumArray object will be instantiated and called as such:
+ * let obj = NumArray::new(nums);
+ * obj.update(i, val);
+ * let ret_2: i32 = obj.sum_range(i, j);
+ */
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_307() {
+        let _empty = NumArray::new(vec![]);
+        let mut tree = NumArray::new(vec![1,1,1,1,1,1,1,1,1,1]);
+        assert_eq!(tree.sum_range(0, 6), 7);
+        tree.update(0, 2);
+        assert_eq!(tree.sum_range(0, 6), 8);
+        tree.update(1, 2);
+        assert_eq!(tree.sum_range(0, 2), 5);
+        tree.update(6, 10);
+        assert_eq!(tree.sum_range(6, 6), 10);
+    }
+}