zoukankan      html  css  js  c++  java
  • LeetCoce 413. Arithmetic Slices

    A sequence of number is called arithmetic if it consists of at least three elements and if the difference between any two consecutive elements is the same.

    For example, these are arithmetic sequence:

    1, 3, 5, 7, 9
    7, 7, 7, 7
    3, -1, -5, -9

    The following sequence is not arithmetic.

    1, 1, 2, 5, 7

    A zero-indexed array A consisting of N numbers is given. A slice of that array is any pair of integers (P, Q) such that 0 <= P < Q < N.

    A slice (P, Q) of array A is called arithmetic if the sequence:
    A[P], A[p + 1], ..., A[Q - 1], A[Q] is arithmetic. In particular, this means that P + 1 < Q.

    The function should return the number of arithmetic slices in the array A.

    Example:

    A = [1, 2, 3, 4]

    return: 3, for 3 arithmetic slices in A: [1, 2, 3], [2, 3, 4] and [1, 2, 3, 4] itself.

    代码一

    class Solution {
    public:
        int numberOfArithmeticSlices(vector<int>& A) {
            if(A.size()<=2) return 0;
            int cnt=0;
            for(int i=0;i<=A.size()-3;i++){
                int temp=A[i+1]-A[i];
                for(int j=i+2;j<A.size();j++)
                    if(A[j]-A[j-1]==temp)
                        cnt++;
                    else 
                        break;
            }
            return cnt;
        }
    };
    

    代码二:动态规划

    class Solution {
    public:
        int numberOfArithmeticSlices(vector<int>& A) {
            int n = A.size();
            if (n < 3) return 0;
            vector<int> dp(n, 0); // dp[i] means the number of arithmetic slices ending with A[i]
            if (A[2]-A[1] == A[1]-A[0]) dp[2] = 1; // if the first three numbers are arithmetic or not
            int result = dp[2];
            for (int i = 3; i < n; ++i) {
                // if A[i-2], A[i-1], A[i] are arithmetic, then the number of arithmetic slices ending with A[i] (dp[i])
                // equals to:
                //      the number of arithmetic slices ending with A[i-1] (dp[i-1], all these arithmetic slices appending A[i] are also arithmetic)
                //      +
                //      A[i-2], A[i-1], A[i] (a brand new arithmetic slice)
                // it is how dp[i] = dp[i-1] + 1 comes
                if (A[i]-A[i-1] == A[i-1]-A[i-2]) 
                    dp[i] = dp[i-1] + 1;
                result += dp[i]; // accumulate all valid slices
            }
            return result;
        }
    };
    
  • 相关阅读:
    Linux下如何查看版本信息
    SUSE12Sp3安装配置.net core 生产环境(2)-安装.NET Core 2.2.1 runtime 并运行.NET代码
    NET CORE Learning
    JWT(JSON Web Token)原理简介
    定性分析与定量分析的异同及优缺点
    《React16免费基础视频教程》【2】
    《React16免费基础视频教程》【1】
    《狂神说-JUC》【3】
    《狂神说-JUC》【2】
    《狂神说-JUC》【1】
  • 原文地址:https://www.cnblogs.com/A-Little-Nut/p/8439091.html
Copyright © 2011-2022 走看看