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📜  以最大绝对和输出与子数组中的元素相对应的所有字符串

📅  最后修改于: 2021-05-17 16:34:44             🧑  作者: Mango

给定一个由N对组成的数组arr [] ,每个对都由一个字符串和一个与该字符串对应的整数组成。任务是找到最大绝对和数组并打印与子数组元素相对应的字符串。

例子:

天真的方法:最简单的方法是生成所有可能的子数组,找到最大的总和子数组。然后,打印与该子数组相对应的字符串。
时间复杂度: O(N 2 )
辅助空间: O(1)

高效的方法:最佳方法是使用经过修改的Kadane算法,以便它可以处理负值并在绝对最小值和绝对最大值之间选择最大值。

请按照以下步骤解决问题:

  1. 初始化 变量res = 0 ,以存储最终答案,而start = 0end = 0,以存储所需子数组的开始和结束索引。
  2. 初始化另外两个变量posPrefixnegPrefix ,以存储先前的正前缀值和负前缀值。
  3. 遍历数组arr []并执行以下操作
    • 如果当前元素为负,并且如果arr [i] + negPrefix> res的值,则更新res的值,开始索引和结束索引。
    • 如果当前元素为正,并且arr [i] + posPrefix> res的值,则更新res的值,开始索引和结束索引。
    • 检查是否将当前元素添加到negPrefix使其大于或等于0 ,然后更新start = i + 1并设置negPrefix = 0,否则,将当前值添加到negPrefix
    • 检查将当前元素添加到posPrefix是否使其小于或等于0 ,然后更新start = i + 1并设置posPrefix = 0,否则,将当前值添加到posPrefix
  4. 最后,遍历[start,end]范围内的数组并打印相应的字符串。

下面是上述方法的实现:

C++
// C++ program for the above approach
 
#include 
using namespace std;
 
// Function to print strings corresponding
// to the elements present in the subarray
// with maximum absolute sum
void maximumAbsSum(pair* arr,
                   int N)
{
    int start = 0, end = 0, res = 0,
        negIndex = 0, posIndex = 0,
        negPrefix = 0, posPrefix = 0;
 
    // Traverse the array
    for (int i = 0; i < N; i++) {
 
        if (arr[i].second < 0) {
 
            // If adding current element
            // to negative
            // prefix makes it > res
            // then update the values
 
            if (res < abs(arr[i].second
                          + negPrefix)) {
 
                res = abs(arr[i].second
                          + negPrefix);
                start = negIndex;
                end = i;
            }
        }
 
        else {
 
            // If adding current element to
            // positive prefix exceeds res
            if (res < abs(arr[i].second
                          + posPrefix)) {
 
                res = abs(arr[i].second
                          + posPrefix);
                start = posIndex;
                end = i;
            }
        }
 
        // Since negPrefix > 0, there is
        // no benefit in adding it to a
        // negative value
        if (negPrefix + arr[i].second > 0) {
 
            negPrefix = 0;
            negIndex = i + 1;
        }
 
        // Since negative + negative
        // generates a larger negative value
        else {
 
            negPrefix += arr[i].second;
        }
 
        // Sicne positive + positive
        // generates a larger positive number
        if (posPrefix + arr[i].second >= 0) {
 
            posPrefix += arr[i].second;
        }
 
        // Since pos_prefix < 0, there is
        // no benefit in adding it to
        // a positive value
        else {
 
            posPrefix = 0;
            posIndex = i + 1;
        }
    }
 
    // Print the corresponding strings
    for (int i = start; i <= end; i++) {
        cout << arr[i].first << " ";
    }
}
 
// Driver Code
int main()
{
    // Given array
    pair arr[] = { { "geeks", 4 },
                                { "for", -3 },
                                { "geeks", 2 },
                                { "tutorial", 3 },
                                { "program", -4 } };
 
    // Size of the array
    int N = sizeof(arr) / sizeof(arr[0]);
 
    // Function call to print
    // string corresponding to
    // maximum absolute subarray sum
    maximumAbsSum(arr, N);
}


Java
// Java program for the above approach
class GFG
{
    static class pair
    {
        E first;
        R second;
        public pair(E first, R second) 
        {
            this.first = first;
            this.second = second;
        }   
    }
   
// Function to print Strings corresponding
// to the elements present in the subarray
// with maximum absolute sum
static void maximumAbsSum(pair []arr,
                   int N)
{
    int start = 0, end = 0, res = 0,
        negIndex = 0, posIndex = 0,
        negPrefix = 0, posPrefix = 0;
 
    // Traverse the array
    for (int i = 0; i < N; i++)
    {
        if (arr[i].second < 0)
        {
 
            // If adding current element
            // to negative
            // prefix makes it > res
            // then update the values
            if (res < Math.abs(arr[i].second
                          + negPrefix)) {
 
                res = Math.abs(arr[i].second
                          + negPrefix);
                start = negIndex;
                end = i;
            }
        }
        else
        {
 
            // If adding current element to
            // positive prefix exceeds res
            if (res < Math.abs(arr[i].second
                          + posPrefix)) {
 
                res = Math.abs(arr[i].second
                          + posPrefix);
                start = posIndex;
                end = i;
            }
        }
 
        // Since negPrefix > 0, there is
        // no benefit in adding it to a
        // negative value
        if (negPrefix + arr[i].second > 0) {
 
            negPrefix = 0;
            negIndex = i + 1;
        }
 
        // Since negative + negative
        // generates a larger negative value
        else {
 
            negPrefix += arr[i].second;
        }
 
        // Sicne positive + positive
        // generates a larger positive number
        if (posPrefix + arr[i].second >= 0) {
 
            posPrefix += arr[i].second;
        }
 
        // Since pos_prefix < 0, there is
        // no benefit in adding it to
        // a positive value
        else {
 
            posPrefix = 0;
            posIndex = i + 1;
        }
    }
 
    // Print the corresponding Strings
    for (int i = start; i <= end; i++) {
        System.out.print(arr[i].first+ " ");
    }
}
 
// Driver Code
@SuppressWarnings("unchecked")
public static void main(String[] args)
{
    // Given array
    @SuppressWarnings("rawtypes")
    pair arr[] = { new pair( "geeks", 4 ),
            new pair( "for", -3 ),
            new pair( "geeks", 2 ),
            new pair( "tutorial", 3 ),
            new pair( "program", -4 ) };
 
    // Size of the array
    int N = arr.length;
 
    // Function call to print
    // String corresponding to
    // maximum absolute subarray sum
    maximumAbsSum(arr, N);
}
}
 
// This code is contributed by shikhasingrajput


Python3
# Python3 program for the above approach
 
# Function to print strings corresponding
# to the elements present in the subarray
# with maximum absolute sum
def maximumAbsSum(arr, N):
    start, end, res = 0, 0, 0
    negIndex, posIndex = 0, 0
    negPrefix, posPrefix = 0, 0
 
    # Traverse the array
    for i in range(N):
        if (arr[i][1] < 0):
 
            # If adding current element
            # to negative
            # prefix makes it > res
            # then update the values
            if (res < abs(arr[i][1] + negPrefix)):
                res = abs(arr[i][1] + negPrefix)
                start = negIndex
                end = i
        else:
 
            # If adding current element to
            # positive prefix exceeds res
            if (res < abs(arr[i][1] + posPrefix)):
                res = abs(arr[i][1] + posPrefix)
                start = posIndex
                end = i
 
        # Since negPrefix > 0, there is
        # no benefit in adding it to a
        # negative value
        if (negPrefix + arr[i][1] > 0):
            negPrefix = 0
            negIndex = i + 1
             
        # Since negative + negative
        # generates a larger negative value
        else:
            negPrefix += arr[i][1]
 
        # Sicne positive + positive
        # generates a larger positive number
        if (posPrefix + arr[i][1] >= 0):
            posPrefix += arr[i][1]
 
        # Since pos_prefix < 0, there is
        # no benefit in adding it to
        # a positive value
        else:
            posPrefix = 0
            posIndex = i + 1
 
    # Print the corresponding strings
    for i in range(start, end + 1):
        print(arr[i][0], end = " ")
 
# Driver Code
if __name__ == '__main__':
   
    # Given array
    arr = [ [ "geeks", 4 ],
            [ "for", -3 ],
            [ "geeks", 2 ],
            [ "tutorial", 3 ],
            [ "program", -4 ] ]
 
    # Size of the array
    N = len(arr)
 
    # Function call to print
    # string corresponding to
    # maximum absolute subarray sum
    maximumAbsSum(arr, N)
 
    # This code is contributed by mohit kumar 29.


C#
// C# program for the above approach
using System;
using System.Collections.Generic;
public class GFG
{
  public class pair
  {
    public string first;
    public int second;
    public pair(string first, int second) 
    {
      this.first = first;
      this.second = second;
    }   
  }
 
  // Function to print Strings corresponding
  // to the elements present in the subarray
  // with maximum absolute sum
  static void maximumAbsSum(pair []arr,
                            int N)
  {
    int start = 0, end = 0, res = 0,
    negIndex = 0, posIndex = 0,
    negPrefix = 0, posPrefix = 0;
 
    // Traverse the array
    for (int i = 0; i < N; i++)
    {
      if (arr[i].second < 0)
      {
 
        // If adding current element
        // to negative
        // prefix makes it > res
        // then update the values
        if (res < Math.Abs(arr[i].second
                           + negPrefix)) {
 
          res = Math.Abs(arr[i].second
                         + negPrefix);
          start = negIndex;
          end = i;
        }
      }
      else
      {
 
        // If adding current element to
        // positive prefix exceeds res
        if (res < Math.Abs(arr[i].second
                           + posPrefix)) {
 
          res = Math.Abs(arr[i].second
                         + posPrefix);
          start = posIndex;
          end = i;
        }
      }
 
      // Since negPrefix > 0, there is
      // no benefit in adding it to a
      // negative value
      if (negPrefix + arr[i].second > 0) {
 
        negPrefix = 0;
        negIndex = i + 1;
      }
 
      // Since negative + negative
      // generates a larger negative value
      else {
 
        negPrefix += arr[i].second;
      }
 
      // Sicne positive + positive
      // generates a larger positive number
      if (posPrefix + arr[i].second >= 0) {
 
        posPrefix += arr[i].second;
      }
 
      // Since pos_prefix < 0, there is
      // no benefit in adding it to
      // a positive value
      else {
 
        posPrefix = 0;
        posIndex = i + 1;
      }
    }
 
    // Print the corresponding Strings
    for (int i = start; i <= end; i++) {
      Console.Write(arr[i].first+ " ");
    }
  }
 
  // Driver Code
  public static void Main(String[] args)
  {
     
    // Given array
    pair []arr = { new pair( "geeks", 4 ),
                  new pair( "for", -3 ),
                  new pair( "geeks", 2 ),
                  new pair( "tutorial", 3 ),
                  new pair( "program", -4 ) };
 
    // Size of the array
    int N = arr.Length;
 
    // Function call to print
    // String corresponding to
    // maximum absolute subarray sum
    maximumAbsSum(arr, N);
  }
}
 
// This code is contributed by Rajput-Ji


输出:
geeks for geeks tutorial

时间复杂度: O(N)
辅助空间: O(1)