算法练习笔记(15)—— 哈希表的练习

来源:互联网 发布:用友软件介绍 编辑:程序博客网 时间:2024/05/17 03:34

当年哈希实在没有学好,实际上真的是非常节省空间的一个数据结构,最近决定多练练!

题目:554. Brick Wall

网址:https://leetcode.com/problems/brick-wall/#/description

描述:

There is a brick wall in front of you. The wall is rectangular and has several rows of bricks. The bricks have the same height but different width. You want to draw a vertical line from the top to the bottom and cross the least bricks.

The brick wall is represented by a list of rows. Each row is a list of integers representing the width of each brick in this row from left to right.

If your line go through the edge of a brick, then the brick is not considered as crossed. You need to find out how to draw the line to cross the least bricks and return the number of crossed bricks.

You cannot draw a line just along one of the two vertical edges of the wall, in which case the line will obviously cross no bricks.

Example:

Input: [[1,2,2,1], [3,1,2], [1,3,2], [2,4], [3,1,2], [1,3,1,1]]Output: 2Explanation: 
分析:

本题考察的是map的应用,当然用数组也可以,但要占用更多的时间与空间,而相对而言哈希的解法也更加直接简单

class Solution {public:    int leastBricks(vector<vector<int>>& wall) {        map <int, int> edges;        auto min_bricks = 0;        for(auto s : wall){            for(int i = 0, w = 0; i < s.size() - 1; i++ ){                w += s[i];                edges[w]++;                min_bricks = max(min_bricks, edges[w]);            }        }        return wall.size() - min_bricks;    }};