Question

我已经阅读了从https://www.geeksforgeeks.org/largest-subarray-having-sum-greater-than-k/

查找最长总和大于k的子数组的方法

    // CPP program to find Longest subarray 
// having average greater than or equal 
// to x. 
#include <bits/stdc++.h> 

using namespace std; 

// Comparison function used to sort preSum vector. 
bool compare(const pair<int, int>& a, const pair<int, int>& b) 
{ 
    if (a.first == b.first) 
        return a.second < b.second;



return a.first < b.first; 
} 

// Function to find index in preSum vector upto which 
// all prefix sum values are less than or equal to val. 
int findInd(vector<pair<int, int> >& preSum, int n, int val) 
{ 

    // Starting and ending index of search space. 
    int l = 0; 
    int h = n - 1; 
    int mid;



// To store required index value. 
int ans = -1; 

// If middle value is less than or equal to 
// val then index can lie in mid+1..n 
// else it lies in 0..mid-1. 
while (l <= h) { 
    mid = (l + h) / 2; 
    if (preSum[mid].first <= val) { 
        ans = mid; 
        l = mid + 1; 
    } 
    else
        h = mid - 1; 
} 

    return ans; 
}



// Function to find Longest subarray having average 
// greater than or equal to x. 
    int LongestSub(int arr[], int n, int x) 
    { 
        int i; 

        // Update array by subtracting x from 
        // each element. 
        for (i = 0; i < n; i++) 

        arr[i] -= x; 

    // Length of Longest subarray. 
    int maxlen = 0; 

    // Vector to store pair of prefix sum 
    // and corresponding ending index value. 
    vector<pair<int, int> > preSum; 

    // To store current value of prefix sum. 
    int sum = 0; 

    // To store minimum index value in range 
    // 0..i of preSum vector. 
    int minInd[n]; 

    // Insert values in preSum vector. 
    for (i = 0; i < n; i++) { 
        sum = sum + arr[i]; 
        preSum.push_back({ sum, i }); 
    } 

    sort(preSum.begin(), preSum.end(), compare); 

    // Update minInd array. 
    minInd[0] = preSum[0].second; 

    for (i = 1; i < n; i++) { 
        minInd[i] = min(minInd[i - 1], preSum[i].second); 
    } 

    sum = 0; 
    for (i = 0; i < n; i++) { 
        sum = sum + arr[i]; 

        // If sum is greater than or equal to 0, 
        // then answer is i+1. 
        if (sum >= 0) 
            maxlen = i + 1; 

        // If sum is less than 0, then find if 
        // there is a prefix array having sum 
        // that needs to be added to current sum to 
        // make its value greater than or equal to 0. 
        // If yes, then compare length of updated 
        // subarray with maximum length found so far. 
        else { 
            int ind = findInd(preSum, n, sum); 
            if (ind != -1 && minInd[ind] < i) 
                maxlen = max(maxlen, i - minInd[ind]); 
        } 
    } 

    return maxlen; 
} 

// Driver code. 
int main() 
{ 
    int arr[] = { -2, 1, 6, -3 }; 
    int n = sizeof(arr) / sizeof(arr[0]); 

    int x = 3; 

    cout << LongestSub(arr, n, x); 
    return 0; 
}

但是我无法从诸如此类的代码中了解一些东西

1）为什么要对前缀和数组进行排序？那会不会干扰数组元素的相对位置？

2）他们使用的minIndex数组有什么用？逐步解释会有所帮助。

谢谢！

注意-我知道StackOverflow上已经存在类似的问题，但是那里的答案提到的是不同的方法，而不是上面链接中的方法。此外，还有另一个问题使用相似的方法来解决相似的问题，但是即使这样也没有帮助。（供参考-Longest Contiguous Subarray with Average Greater than or Equal to k）

查找总和大于k的最长子数组

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