zoukankan      html  css  js  c++  java
  • Leetcode: Maximum Size Subarray Sum Equals k

    Given an array nums and a target value k, find the maximum length of a subarray that sums to k. If there isn't one, return 0 instead.
    
    Example 1:
    Given nums = [1, -1, 5, -2, 3], k = 3,
    return 4. (because the subarray [1, -1, 5, -2] sums to 3 and is the longest)
    
    Example 2:
    Given nums = [-2, -1, 2, 1], k = 1,
    return 2. (because the subarray [-1, 2] sums to 1 and is the longest)
    
    Follow Up:
    Can you do it in O(n) time?

    Like the other subarray sum problems Lintcode: Subarray Sum closest

    Use a HashMap to keep track of the sum from index 0 to index i, use it as the key, and use the current index as the value

    build the hashmap: scan from left to write, if the current sum does not exist in the hashmap, put it in. If the current sum does exist in Hashmap, do not replace or add to the older value, simply do not update. Because this value might be the left index of our subarray in later comparison. We are looking for the longest subarray so we want the left index to be the smaller the better. 

    Every time we read a number in the array, we check to see if map.containsKey(num-k), if yes, try to update the maxLen.

     1 public class Solution {
     2     public int maxSubArrayLen(int[] nums, int k) {
     3         if (nums==null || nums.length==0) return 0;
     4         HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();
     5         map.put(0, -1);
     6         int sum = 0;
     7         int maxLen = Integer.MIN_VALUE;
     8         for (int i=0; i<nums.length; i++) {
     9             sum += nums[i];
    10             if (!map.containsKey(sum)) {
    11                 map.put(sum, i);
    12             }
    13             if (map.containsKey(sum-k)) {
    14                 int index = map.get(sum-k);
    15                 maxLen = Math.max(maxLen, i-index);
    16             }
    17         }
    18         return maxLen==Integer.MIN_VALUE? 0 : maxLen;
    19     }
    20 }
  • 相关阅读:
    C# 删除文件夹
    XML操作类
    C# winform 安装程序打包(自定义操作)
    复制Datatable结构和数据,并按条件进行筛选
    Sql_Case_When
    C# using 与Trycatchfinally的区别和用法
    Winform datagridview Excel 导入导出
    矩阵树定理学习笔记
    minmax容斥笔记及例题
    平衡树学习笔记
  • 原文地址:https://www.cnblogs.com/EdwardLiu/p/5104280.html
Copyright © 2011-2022 走看看