牛客NC166 连续子数组的最大和(二)【中等 前缀和数组+动态规划 Java/Go/PHP/C++】

题目

题目链接：

https://www.nowcoder.com/practice/11662ff51a714bbd8de809a89c481e21

思路

前缀和数组+动态规划

Java代码

import java.util.*;


public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param array int整型一维数组
     * @return int整型一维数组
     */
    public int[] FindGreatestSumOfSubArray (int[] array) {
        //前缀和+动态规划
        int n = array.length;
        if (n <= 1) return array;

        int[] presum = new int[n + 1]; //前缀和
        for (int i = 0; i < n; i++) {
            presum[i + 1] = presum[i] + array[i];
        }
        int[] dp = new int[n];
        dp[0] = array[0];
        int pre = array[0];
        int maxSum = array[0];
        int maxSumEnd = 0;
       //存放最的子数组和的子数组下标列表
        List<Integer> maxsumll = new ArrayList<>();
        for (int i = 1; i < n ; i++) {
            int p1 = array[i];
            int p2 = array[i] + pre;
            int cur = Math.max(p1, p2);
            //maxSum=Math.max(maxSum,cur);

            if (maxSum <= cur) {
                if (maxSum < cur) {
                    maxsumll.clear();

                }
                maxsumll.add(i);
                maxSum = cur;
                maxSumEnd = i;
            }
            pre = cur;
        }

        //System.out.println(maxSum+", "+maxSumEnd);
        //System.out.println(sumIdx);
        int maxSize = 0;
        int maxSizeIdx = 0;
        for (Integer idx : maxsumll) {

            //for (int i = idx; i <=idx ; i++) {
            for (int j = 0; j <= idx ; j++) {
                if (presum[idx + 1] - presum[j] == maxSum) {
                    //size=Math.max(size,idx+1-j);
                    if (maxSize < idx + 1 - j) {
                        maxSize = idx + 1 - j;
                        maxSizeIdx = idx;
                    }
                    break;
                }
                //  }
            }
        }

        // System.out.println("size:"+ maxSize+" maxSizeidx:"+ maxSizeIdx);
        int[] ans = new int[maxSize];
        for (int i = 0; i < maxSize ; i++) {
            ans[i] = array[maxSizeIdx - maxSize + 1 + i];
        }
        return ans;
    }
}

Go代码

package main

/**
 * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
 *
 *
 * @param array int整型一维数组
 * @return int整型一维数组
 */
func FindGreatestSumOfSubArray(array []int) []int {
	//前缀和+动态规划
	n := len(array)
	if n <= 1 {
		return array
	}

	presum := make([]int, n+1)
	for i := 0; i < n; i++ {
		presum[i+1] = presum[i] + array[i]
	}

	pre := array[0]
	maxSum := array[0]
	maxSumll := []int{} //存放最的子数组和的子数组下标列表

	for i := 1; i < n; i++ {
		p1 := array[i]
		p2 := array[i] + pre

		cur := p1
		if cur < p2 {
			cur = p2
		}

		if maxSum <= cur {
			if maxSum < cur {
				maxSumll = []int{}
			}
			maxSum = cur
			maxSumll = append(maxSumll, i)
		}

		pre = cur
	}

	maxSize := 0
	maxSizeIdx := 0

	for _, idx := range maxSumll {
		for j := 0; j <= idx; j++ {
			if presum[idx+1]-presum[j] == maxSum {
				if maxSize < idx+1-j {
					maxSize = idx + 1 - j
					maxSizeIdx = idx
				}

				break
			}

		}
	}

	ans := make([]int, maxSize)
	for i := 0; i < maxSize; i++ {
		ans[i] = array[maxSizeIdx+1-maxSize+i]
	}
	return ans
}

PHP代码

<?php


/**
 * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
 *
 * 
 * @param array int整型一维数组 
 * @return int整型一维数组
 */
function FindGreatestSumOfSubArray( $array )
{
    //前缀和+动态规划
    $n= count($array);
    if($n <=1){
        return $array;
    }

    $presum = [0=>0];
    for($i=0;$i<$n;$i++){
        $presum[$i+1] = $presum[$i]+$array[$i];
    }

    $pre = $array[0];
    $max = $array[0];
    $list = array(); //存放$max对应的子数组的结束下标

    for($i=1;$i<$n;$i++){
        $cur = $array[$i];
        $p2 = $array[$i]+$pre;
        if($cur < $p2){
            $cur = $p2;
        }

        if($max<=$cur){
            if($max<$cur) {
                $list = array();
            }
            $list[count($list)] = $i;
            $max = $cur;
        }

        $pre=$cur;
    }


    $maxLen =0;
    $maxLenIdx =0;

    foreach ($list as $idx){
        for($j=0;$j<=$idx;$j++){
           if($presum[$idx+1] -$presum[$j] ==$max){
               if($maxLen < $idx+1-$j){
                   $maxLen = $idx+1-$j;
                   $maxLenIdx = $idx;
               }
               break;
           }
        }
    }


    $ans=[];
    for($i=0;$i<$maxLen;$i++){
        $ans[$i] = $array[$maxLenIdx-$maxLen+1+$i];
    }
    return $ans;
}

C++代码

class Solution {
  public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param array int整型vector
     * @return int整型vector
     */
    vector<int> FindGreatestSumOfSubArray(vector<int>& array) {
        //前缀和+动态规划
        int n = array.size();
        if (n <= 1)
            return array;

        //前缀和
        vector<int> presum(n + 1, 0);
        for (int i = 0; i < n; i++) {
            presum[i + 1] = presum[i] + array[i];
        }

        int pre = array[0];
        int max = array[0]; //最大的子数组和
        vector<int> list; //存放max对应的子数组的下标列表
        for (int i = 1; i < n; i++) {
            int p1 = array[i];
            int p2 = array[i] + pre;
            int cur = p1;
            if (cur < p2) {
                cur = p2;
            }

            if (max <= cur) {
                if (max < cur) {
                    list.clear();
                }
                max = cur;
                list.push_back(i);
            }

            pre = cur;
        }


        int maxLen = 0;
        int maxLenIdx = 0;
        for (int i = 0; i < list.size(); i++) {
            int idx = list[i];
            for (int j = 0; j <= idx; j++) {
                if (presum[idx + 1] - presum[j] == max) {
                    if (maxLen < idx + 1 - j) {
                        maxLen = idx + 1 - j;
                        maxLenIdx = idx;
                    }
                    break;
                }
            }
        }


        vector<int> ans(maxLen);
        for (int i = 0; i < maxLen; i++) {
            ans[i] = array[maxLenIdx - maxLen + 1 + i];
        }

        return ans;
    }
};