41 lines
1.4 KiB
Rust
41 lines
1.4 KiB
Rust
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struct NumMatrix {
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sums_matrix: Vec<Vec<i32>>
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}
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/**
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* `&self` means the method takes an immutable reference.
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* If you need a mutable reference, change it to `&mut self` instead.
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*/
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impl NumMatrix {
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// Generate an accumulating sum matrix in-place
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// O(1) extra memory
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fn new(mut matrix: Vec<Vec<i32>>) -> Self {
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for row in (0..matrix.len()) {
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let mut acc = 0;
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for col in (0..matrix[0].len()) {
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acc += matrix[row][col];
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matrix[row][col] = acc;
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if row != 0 {
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matrix[row][col] += matrix[row-1][col];
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}
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}
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}
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NumMatrix { sums_matrix: matrix }
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}
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// Use the accumulating sums to get the sum of the region
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// Space: O(1), Time: O(1)
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fn sum_region(&self, row1: i32, col1: i32, row2: i32, col2: i32) -> i32 {
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let top_rec = if row1 == 0 { 0 } else { self.sums_matrix[row1 as usize - 1][col2 as usize] };
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let left_rec = if col1 == 0 { 0 } else { self.sums_matrix[row2 as usize][col1 as usize - 1] };
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let rec_overlap = if row1 == 0 || col1 == 0 { 0 } else { self.sums_matrix[row1 as usize - 1][col1 as usize - 1] };
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self.sums_matrix[row2 as usize][col2 as usize] - top_rec - left_rec + rec_overlap
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}
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}
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/**
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* Your NumMatrix object will be instantiated and called as such:
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* let obj = NumMatrix::new(matrix);
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* let ret_1: i32 = obj.sum_region(row1, col1, row2, col2);
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*/
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