# problem0304

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Published: Jul 25, 2019 License: MIT

### 304. Range Sum Query 2D - Immutable

#### 题目

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).

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.

## Documentation ¶

### Constants ¶

This section is empty.

### Variables ¶

This section is empty.

### Functions ¶

This section is empty.

### Types ¶

#### type NumMatrix ¶

```type NumMatrix struct {
// contains filtered or unexported fields
}```

NumMatrix 包含了需要求和的矩阵

#### func Constructor ¶

`func Constructor(matrix [][]int) NumMatrix`

Constructor 创建 NumMatrix

#### func (*NumMatrix) SumRegion ¶

`func (nm *NumMatrix) SumRegion(row1 int, col1 int, row2 int, col2 int) int`

SumRegion 求和