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[LeetCode] Range Sum Query - Immutable & Range Sum Query 2D - Immutable

时间:2015-11-16 19:38:15      阅读:246      评论:0      收藏:0      [点我收藏+]

Range Sum Query - Immutable

Given an integer array nums, find the sum of the elements between indices i and j (i ≤ j), inclusive.

Example:

Given nums = [-2, 0, 3, -5, 2, -1]

sumRange(0, 2) -> 1
sumRange(2, 5) -> -1
sumRange(0, 5) -> -3

Note:

  1. You may assume that the array does not change.
  2. There are many calls to sumRange function.
 1 class NumArray {
 2 private:
 3     vector<int> acc;
 4     
 5 public:
 6     NumArray(vector<int> &nums) {
 7         acc.push_back(0);
 8         for (auto n : nums) {
 9             acc.push_back(acc.back() + n);
10         }
11     }
12 
13     int sumRange(int i, int j) {
14         return acc[j + 1] - acc[i];
15     }
16 };
17 
18 
19 // Your NumArray object will be instantiated and called as such:
20 // NumArray numArray(nums);
21 // numArray.sumRange(0, 1);
22 // numArray.sumRange(1, 2);

 

Range Sum Query 2D - Immutable

Given a 2D matrix matrix, find the sum of the elements inside the rectangle defined by its upper left corner (row1, col1) and lower right corner (row2, col2).

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The above rectangle (with the red border) is defined by (row1, col1) = (2, 1) and (row2, col2) = (4, 3), which contains sum = 8.

Example:

Given matrix = [
  [3, 0, 1, 4, 2],
  [5, 6, 3, 2, 1],
  [1, 2, 0, 1, 5],
  [4, 1, 0, 1, 7],
  [1, 0, 3, 0, 5]
]

sumRegion(2, 1, 4, 3) -> 8
sumRegion(1, 1, 2, 2) -> 11
sumRegion(1, 2, 2, 4) -> 12

Note:

  1. You may assume that the matrix does not change.
  2. There are many calls to sumRegion function.
  3. You may assume that row1 ≤ row2 and col1 ≤ col2.

 

 1 class NumMatrix {
 2 private:
 3     vector<vector<int>> acc;
 4 public:
 5     NumMatrix(vector<vector<int>> &matrix) {
 6         if (matrix.empty()) return;
 7         int n = matrix.size(), m = matrix[0].size();
 8         acc.resize(n + 1, vector<int>(m + 1));
 9         for (int i = 0; i <= n; ++i) acc[i][0] = 0;
10         for (int j = 0; j <= m; ++j) acc[0][j] = 0;
11         for (int i = 1; i <= n; ++i) {
12             for (int j = 1; j <= m; ++j) {
13                 acc[i][j] = acc[i][j-1] + acc[i-1][j] - acc[i-1][j-1] + matrix[i-1][j-1];
14             }
15         } 
16     }
17 
18     int sumRegion(int row1, int col1, int row2, int col2) {
19         return acc[row2+1][col2+1] - acc[row1][col2+1] - acc[row2+1][col1] + acc[row1][col1];
20     }
21 };
22 
23 
24 // Your NumMatrix object will be instantiated and called as such:
25 // NumMatrix numMatrix(matrix);
26 // numMatrix.sumRegion(0, 1, 2, 3);
27 // numMatrix.sumRegion(1, 2, 3, 4);

 

[LeetCode] Range Sum Query - Immutable & Range Sum Query 2D - Immutable

原文:http://www.cnblogs.com/easonliu/p/4969767.html

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