力扣209.长度最小的数组
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模版滑窗求最小 
            
            
              cpp
              
              
            
          
            class Solution {
  public:
      int minSubArrayLen(int target, vector<int>& nums) {
          int n = nums.size(),res=n+1;
          int sum = 0;
          for(int i=0,j=0;i<n;i++)
          {
              sum += nums[i];
              //尽可能缩小区间
              while(sum - nums[j] >= target)
              {
                  sum -= nums[j++];
              }
              if(sum >= target) res = min(res,i-j+1);
          }
          if(res == n+1) return 0;
          else return res;
      }
  };