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没有明白：

287 鸽巢原理

Subarray Sum Equals K

class Solution {public:    int subarraySum(vector<int>& nums, int k) {        int sum=0;        map<int,int> p;        int count=0;        p[0]=1;//不可缺少这一项        for(int i=0;i<nums.size();i++)        {            sum+=nums[i];            if(p.find(sum-k)!=p.end()) {//为什么加了这个就不通过                count+=p[sum-k];            p[sum]++;        }        return count;    }    }};

413. Arithmetic Slices 这种方法为什么不对？

class Solution {public:    int numberOfArithmeticSlices(vector<int>& A) {                int n=A.size();        if(n<=2) return 0;        vector<int> sum(n+1,0);        //求累加和数组        for(int i=1;i<=n;i++)        sum[i]=sum[i-1]+A[i-1];        int count=0;        for(int i=3;i<=n;i++)        {            for(int k=3;i-k>=0;k++)            {                int cursum=sum[i]-sum[i-k];                if((cursum-k*A[i-k])%(k*(k-1)/2)==0)                count++;            }        }          return count;      }};

209. Minimum Size Subarray Sum

int minSubArrayLen(int s, vector<int>& nums){    int n = nums.size();    if (n == 0)        return 0;    int ans = INT_MAX;    vector<int> sums(n + 1, 0); //size = n+1 for easier calculations    //sums[0]=0 : Meaning that it is the sum of first 0 elements    //sums[1]=A[0] : Sum of first 1 elements    //ans so on...    for (int i = 1; i <= n; i++)        sums[i] = sums[i - 1] + nums[i - 1];    for (int i = 1; i <= n; i++) {        int to_find = s + sums[i - 1];        auto bound = lower_bound(sums.begin(), sums.end(), to_find);        if (bound != sums.end()) {            ans = min(ans, static_cast<int>(bound - (sums.begin() + i - 1)));        }    }    return (ans != INT_MAX) ? ans : 0;}

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