zoukankan      html  css  js  c++  java
  • 304. Range Sum Query 2D

    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).

    Range Sum Query 2D
    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.

    Approach #1: DP. [C++]

    class NumMatrix {
    public:
        NumMatrix(vector<vector<int>> matrix) {
            int m = matrix.size();
            int n = m > 0 ? matrix[0].size() : 0;
            
            sums.resize(m+1, vector<int>(n+1, 0));
            
            for (int i = 1; i <= m; ++i) {
                for (int j = 1; j <= n; ++j) {
                    sums[i][j] = matrix[i-1][j-1]
                               + sums[i-1][j]
                               + sums[i][j-1]
                               - sums[i-1][j-1];
                    //cout << "sums[" << i << "][" << j << "] = " << sums[i][j] << " ";
                }
                //cout << endl;
            }
        }
        
        int sumRegion(int row1, int col1, int row2, int col2) {
            row2++, col2++;
            return sums[row2][col2] - sums[row2][col1] - sums[row1][col2] + sums[row1][col1];
        }
        
    private:
        vector<vector<int>> sums;
        bool flag = true;
    };
    
    /**
     * Your NumMatrix object will be instantiated and called as such:
     * NumMatrix obj = new NumMatrix(matrix);
     * int param_1 = obj.sumRegion(row1,col1,row2,col2);
     */
    

      

    Analysis:

    If the row = 0, we can't use matrix[0].size(). otherwise the compiler will report error.

    永远渴望,大智若愚(stay hungry, stay foolish)
  • 相关阅读:
    Cobbler-自动化部署神器
    ssh,公钥和私钥,远程复制
    VIM文本替换命令
    #!/usr/bin/env bash和#!/usr/bin/bash的比较
    [PXE] Linux(centos6)中PXE 服务器搭建,PXE安装、启动及PXE理论详解
    mount命令中offset参数的意义
    ironic+nova详解
    【ironic】ironic介绍与原理
    在进行商业运算时解决BigDecimal的精度丢失问题
    后台商品搜索功能开发SQL
  • 原文地址:https://www.cnblogs.com/h-hkai/p/10386269.html
Copyright © 2011-2022 走看看