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| 1 | +/** |
| 2 | + * [307] Range Sum Query - Mutable |
| 3 | + * |
| 4 | + * Given an integer array nums, find the sum of the elements between indices i and j (i ≤ j), inclusive. |
| 5 | + * |
| 6 | + * The update(i, val) function modifies nums by updating the element at index i to val. |
| 7 | + * |
| 8 | + * Example: |
| 9 | + * |
| 10 | + * |
| 11 | + * Given nums = [1, 3, 5] |
| 12 | + * |
| 13 | + * sumRange(0, 2) -> 9 |
| 14 | + * update(1, 2) |
| 15 | + * sumRange(0, 2) -> 8 |
| 16 | + * |
| 17 | + * |
| 18 | + * Note: |
| 19 | + * |
| 20 | + * <ol> |
| 21 | + * The array is only modifiable by the update function. |
| 22 | + * You may assume the number of calls to update and sumRange function is distributed evenly. |
| 23 | + * </ol> |
| 24 | + * |
| 25 | + */ |
| 26 | +pub struct Solution {} |
| 27 | + |
| 28 | +// Segement Tree |
| 29 | +// |
| 30 | +// N[0:6] |
| 31 | +// / \ |
| 32 | +// / \ |
| 33 | +// N[0:3] N[4:6] |
| 34 | +// / \ / \ |
| 35 | +// N[0:1] N[2:3] N[4:5] N[6] |
| 36 | +// / \ / \ / \ |
| 37 | +// N[0] N[1] N[2] N[3] N[4] N[5] |
| 38 | +// |
| 39 | +// submission codes start here |
| 40 | + |
| 41 | +struct NumArray { |
| 42 | + tree: Vec<i32>, |
| 43 | + n: usize, |
| 44 | +} |
| 45 | + |
| 46 | +/** |
| 47 | + * `&self` means the method takes an immutable reference. |
| 48 | + * If you need a mutable reference, change it to `&mut self` instead. |
| 49 | + */ |
| 50 | +impl NumArray { |
| 51 | + fn new(nums: Vec<i32>) -> Self { |
| 52 | + let n = nums.len(); |
| 53 | + let mut tree = vec![0; 4*n]; |
| 54 | + if n > 0 { |
| 55 | + NumArray::build(1, 0, n-1, &mut tree, &nums); |
| 56 | + } |
| 57 | + NumArray{tree: tree, n: n} |
| 58 | + } |
| 59 | + |
| 60 | + fn update(&mut self, i: i32, val: i32) { |
| 61 | + NumArray::update_internal(i as usize, val, 1, 0, self.n-1, &mut self.tree); |
| 62 | + } |
| 63 | + |
| 64 | + fn sum_range(&self, i: i32, j: i32) -> i32 { |
| 65 | + NumArray::sum(1, 0, self.n-1, i as usize, j as usize, &self.tree) |
| 66 | + } |
| 67 | + |
| 68 | + fn build(node: usize, start: usize, end: usize, tree: &mut Vec<i32>, nums: &Vec<i32>) { |
| 69 | + if start == end { |
| 70 | + tree[node] = nums[start]; |
| 71 | + } else { |
| 72 | + let mid = (start + end) / 2; |
| 73 | + NumArray::build(2*node, start, mid, tree, nums); |
| 74 | + NumArray::build(2*node+1, mid+1, end, tree, nums); |
| 75 | + tree[node] = tree[2*node] + tree[2*node+1]; |
| 76 | + } |
| 77 | + } |
| 78 | + |
| 79 | + fn update_internal(i: usize, val: i32, node: usize, start: usize, end: usize, tree: &mut Vec<i32>) { |
| 80 | + if start == end { |
| 81 | + tree[node] = val; |
| 82 | + } else { |
| 83 | + let mid = (start + end) / 2; |
| 84 | + if i <= mid { |
| 85 | + NumArray::update_internal(i, val, 2*node, start, mid, tree); |
| 86 | + } else { |
| 87 | + NumArray::update_internal(i, val, 2*node+1, mid+1, end, tree); |
| 88 | + } |
| 89 | + tree[node] = tree[2*node] + tree[2*node+1]; |
| 90 | + } |
| 91 | + } |
| 92 | + |
| 93 | + fn sum(node: usize, start: usize, end: usize, left: usize, right: usize, tree: &Vec<i32>) -> i32 { |
| 94 | + if right < start || left > end { |
| 95 | + // not in range |
| 96 | + 0 |
| 97 | + } else if left <= start && end <= right { |
| 98 | + // completely in range |
| 99 | + tree[node] |
| 100 | + } else { |
| 101 | + // partially in range |
| 102 | + let mid = (start + end) / 2; |
| 103 | + NumArray::sum(2*node, start, mid, left, right, tree) + |
| 104 | + NumArray::sum(2*node+1, mid+1, end, left, right ,tree) |
| 105 | + } |
| 106 | + } |
| 107 | +} |
| 108 | + |
| 109 | +/** |
| 110 | + * Your NumArray object will be instantiated and called as such: |
| 111 | + * let obj = NumArray::new(nums); |
| 112 | + * obj.update(i, val); |
| 113 | + * let ret_2: i32 = obj.sum_range(i, j); |
| 114 | + */ |
| 115 | + |
| 116 | +// submission codes end |
| 117 | + |
| 118 | +#[cfg(test)] |
| 119 | +mod tests { |
| 120 | + use super::*; |
| 121 | + |
| 122 | + #[test] |
| 123 | + fn test_307() { |
| 124 | + let _empty = NumArray::new(vec![]); |
| 125 | + let mut tree = NumArray::new(vec![1,1,1,1,1,1,1,1,1,1]); |
| 126 | + assert_eq!(tree.sum_range(0, 6), 7); |
| 127 | + tree.update(0, 2); |
| 128 | + assert_eq!(tree.sum_range(0, 6), 8); |
| 129 | + tree.update(1, 2); |
| 130 | + assert_eq!(tree.sum_range(0, 2), 5); |
| 131 | + tree.update(6, 10); |
| 132 | + assert_eq!(tree.sum_range(6, 6), 10); |
| 133 | + } |
| 134 | +} |
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