给定一个包含整数的大小为n的数组arr[] 。问题是找到总和等于给定值k的最长子数组的长度。
例子：
Input : arr[] = { 10, 5, 2, 7, 1, 9 },
k = 15
Output : 4
The sub-array is {5, 2, 7, 1}.
Input : arr[] = {-5, 8, -14, 2, 4, 12},
k = -5
Output : 5朴素方法：考虑所有子数组的总和并返回总和为“k”的最长子数组的长度。时间复杂度为 O(n^2)。
有效的方法：以下是步骤：
- 初始化sum = 0 和maxLen = 0。
- 创建一个具有(sum, index)元组的哈希表。
- 对于 i = 0 到 n-1，执行以下步骤：
- 将 arr[i] 累加到sum 。
- 如果 sum == k，更新maxLen = i+1。
- 检查哈希表中是否存在sum 。如果不存在，则将其作为(sum, i)对添加到哈希表中。
- 检查(sum-k)是否存在于哈希表中。如果存在，则从哈希表中获取(sum-k)的索引作为index 。现在检查是否 maxLen < (i-index)，然后更新maxLen = (i-index)。
- 返回maxLen 。
C++
// C++ implementation to find the length
// of longest subarray having sum k
#include
using namespace std;
// function to find the length of longest
// subarray having sum k
int lenOfLongSubarr(int arr[],
int n,
int k)
{
// unordered_map 'um' implemented
// as hash table
unordered_map um;
int sum = 0, maxLen = 0;
// traverse the given array
for (int i = 0; i < n; i++) {
// accumulate sum
sum += arr[i];
// when subarray starts from index '0'
if (sum == k)
maxLen = i + 1;
// make an entry for 'sum' if it is
// not present in 'um'
if (um.find(sum) == um.end())
um[sum] = i;
// check if 'sum-k' is present in 'um'
// or not
if (um.find(sum - k) != um.end()) {
// update maxLength
if (maxLen < (i - um[sum - k]))
maxLen = i - um[sum - k];
}
}
// required maximum length
return maxLen;
}
// Driver Code
int main()
{
int arr[] = {10, 5, 2, 7, 1, 9};
int n = sizeof(arr) / sizeof(arr[0]);
int k = 15;
cout << "Length = "
<< lenOfLongSubarr(arr, n, k);
return 0;
} Java
// Java implementation to find the length
// of longest subarray having sum k
import java.io.*;
import java.util.*;
class GFG {
// function to find the length of longest
// subarray having sum k
static int lenOfLongSubarr(int[] arr, int n, int k)
{
// HashMap to store (sum, index) tuples
HashMap map = new HashMap<>();
int sum = 0, maxLen = 0;
// traverse the given array
for (int i = 0; i < n; i++) {
// accumulate sum
sum += arr[i];
// when subarray starts from index '0'
if (sum == k)
maxLen = i + 1;
// make an entry for 'sum' if it is
// not present in 'map'
if (!map.containsKey(sum)) {
map.put(sum, i);
}
// check if 'sum-k' is present in 'map'
// or not
if (map.containsKey(sum - k)) {
// update maxLength
if (maxLen < (i - map.get(sum - k)))
maxLen = i - map.get(sum - k);
}
}
return maxLen;
}
// Driver code
public static void main(String args[])
{
int[] arr = {10, 5, 2, 7, 1, 9};
int n = arr.length;
int k = 15;
System.out.println("Length = " +
lenOfLongSubarr(arr, n, k));
}
}
// This code is contibuted by rachana soma Python3
# Python3 implementation to find the length
# of longest subArray having sum k
# function to find the longest
# subarray having sum k
def lenOfLongSubarr(arr, n, k):
# dictionary mydict implemented
# as hash map
mydict = dict()
# Initialize sum and maxLen with 0
sum = 0
maxLen = 0
# traverse the given array
for i in range(n):
# accumulate the sum
sum += arr[i]
# when subArray starts from index '0'
if (sum == k):
maxLen = i + 1
# check if 'sum-k' is present in
# mydict or not
elif (sum - k) in mydict:
maxLen = max(maxLen, i - mydict[sum - k])
# if sum is not present in dictionary
# push it in the dictionary with its index
if sum not in mydict:
mydict[sum] = i
return maxLen
# Driver Code
if __name__ == '__main__':
arr = [10, 5, 2, 7, 1, 9]
n = len(arr)
k = 15
print("Length =", lenOfLongSubarr(arr, n, k))
# This code is contributed by
# chaudhary_19 (Mayank Chaudhary)C#
// C# implementation to find the length
// of longest subarray having sum k
using System;
using System.Collections.Generic;
class GFG
{
// function to find the length of longest
// subarray having sum k
static int lenOfLongSubarr(int[] arr,
int n, int k)
{
// HashMap to store (sum, index) tuples
Dictionary map = new Dictionary();
int sum = 0, maxLen = 0;
// traverse the given array
for (int i = 0; i < n; i++)
{
// accumulate sum
sum += arr[i];
// when subarray starts from index '0'
if (sum == k)
maxLen = i + 1;
// make an entry for 'sum' if it is
// not present in 'map'
if (!map.ContainsKey(sum))
{
map.Add(sum, i);
}
// check if 'sum-k' is present in 'map'
// or not
if (map.ContainsKey(sum - k))
{
// update maxLength
if (maxLen < (i - map[sum - k]))
maxLen = i - map[sum - k];
}
}
return maxLen;
}
// Driver code
public static void Main()
{
int[] arr = {10, 5, 2, 7, 1, 9};
int n = arr.Length;
int k = 15;
Console.WriteLine("Length = " +
lenOfLongSubarr(arr, n, k));
}
}
// This code is contibuted by PrinciRaj1992 Javascript
输出：
Length = 4时间复杂度： O(n)。
辅助空间： O(n)。
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