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  • 力扣算法题—053最大子序之和

     1 #include "000库函数.h"
     2 
     3 //一想到又是遍历
     4 class Solution {
     5 public:
     6     int maxSubArray(vector<int>& nums) {
     7         int res=nums[0];
     8         for (int i = 0; i < nums.size(); ++i) {
     9             int sum = nums[i];
    10             res = res > sum ? res : sum;
    11             for (int j = i + 1; j < nums.size(); ++j) {
    12                 sum += nums[j];
    13                 res = res > sum ? res : sum;
    14             }
    15         }
    16         return res;
    17     }
    18 };
    19 
    20 //使用滑窗来做
    21 class Solution {
    22 public:
    23     int maxSubArray(vector<int>& nums) {
    24         int res = nums[0];
    25         int sum = -1;
    26         for (auto a : nums) {
    27             sum = max(a, sum + a);
    28             res = max(res, sum);
    29         }
    30         return res;
    31     }
    32 };
    33 
    34 
    35 
    36 //用分治法来计算,将数组一分为二,从中间来开始遍历
    37 
    38 class Solution {
    39 public:
    40     int maxSubArray(vector<int>& nums) {
    41         return helper(nums, 0, nums.size() - 1);
    42     }
    43     int helper(vector<int>nums, int left, int right) {
    44         if (left >= right)return nums[left];
    45         int mid = (left + right) / 2;
    46         int lmax = helper(nums, left, mid - 1);//左移
    47         int rmax = helper(nums, mid + 1, right);//右移
    48         int mmax = nums[mid], t = mmax;
    49         for (int i = mid - 1; i >= left; --i) {//左移计算
    50             t += nums[i];
    51             mmax = mmax > t ? mmax : t;
    52         }
    53         t = mmax;
    54         for (int i = mid + 1; i <= right; ++i) {
    55             t += nums[i];
    56             mmax = mmax > t ? mmax : t;
    57         }
    58         return mmax > (rmax > lmax ? rmax : lmax) ? mmax : (rmax > lmax ? rmax : lmax);
    59     }
    60 };
    61 
    62 void T053() {
    63     Solution s;
    64     vector<int>v;
    65     v = { -2, 1, -3, 4, -1, 2, 1, -5, 4 };
    66     cout << s.maxSubArray(v) << endl;
    67 }
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  • 原文地址:https://www.cnblogs.com/zzw1024/p/10631471.html
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