代码随想录算法训练营 Day5 | Hot100 | 53.最大子数组和 56.合并区间 189.轮转数组 238.除自身以外数组的乘积

Day5

休息，看看hot100

类DP或者前缀和问题

53. Maximum Subarray

class Solution {
public:
    int maxSubArray(vector<int>& nums) {
        if(nums.size() == 1)
            return nums[0];
        int currSum = 0;
        int ans = nums[0];
        for(int i=0; i<nums.size(); ++i)
        {
            currSum += nums[i];
            ans = max(ans, currSum);
            if(currSum <= 0)
                currSum = 0;
        }
        return ans;
    }
};

56. Merge Intervals

class Solution {
public:
    static bool cmp(vector<int>& v1, vector<int> &v2)
    {
        return v1[0] < v2[0];
    }
    vector<vector<int>> merged;
    vector<vector<int>> merge(vector<vector<int>>& intervals) {
        if(intervals.size() == 1)
            return intervals;
        sort(intervals.begin(), intervals.end(), cmp);

        for(int i=1; i<intervals.size(); ++i)
        {
            if(intervals[i][0] > intervals[i-1][1])
            {
                merged.push_back(intervals[i-1]);
            }
            else if(intervals[i][0] <= intervals[i-1][1])
            {
                intervals[i][0] = intervals[i-1][0];
                if(intervals[i][1] < intervals[i-1][1])
                {
                    intervals[i][1] = intervals[i-1][1];
                }
            }
        }
        merged.push_back(intervals[intervals.size()-1]);
        return merged;
    }
};

189. Rotate Array

class Solution {
public:
    void rotate(vector<int>& nums, int k) {
        k = k % nums.size();
        reverse(nums.begin(), nums.end());
        reverse(nums.begin(), nums.begin()+k);
        reverse(nums.begin()+k, nums.end());
    }
};

238. Product of Array Except Self

class Solution {
public:
    vector<int> productExceptSelf(vector<int>& nums) {
        int length = nums.size();
        vector<int> answer(length);

        answer[0] = 1;
        for (int i = 1; i < length; i++) {
            answer[i] = nums[i - 1] * answer[i - 1];
        }

        int R = 1;
        for (int i = length - 1; i >= 0; i--) {
            answer[i] = answer[i] * R;
            R *= nums[i];
        }

        return answer;
    }
};