leetcode_209. Minimum Size Subarray Sum

https://leetcode.com/problems/minimum-size-subarray-sum/#/description

Given an array of n positive integers and a positive integer s, find the minimal length of a contiguous subarray of which the sum ≥ s.
If there isn't one, return 0 instead.

For example, given the array 

[2,3,1,2,4,3]

 and 

s
= 7

,

the subarray 

[4,3]

 has the minimal length under the problem constraint.

题意：给你一个数组，问最短的子序列大于s的长度是几？

做法：首先记录一下第一个到第i个的和，然后for for两次肯定可以做出来了，不过估计要超时，所以得优化。

          那就能想到，比如从i到j满足大于s了，那么从第i+1个位置肯定要到j或者以上才能大于s

class Solution {
public:
int minSubArrayLen(int s, vector<int>& nums) {
int length = nums.size();
if(length==0)
{
return 0;
}
int sum[length+1];
sum[0]=nums[0];
int ans=1<<30;
for(int i=1;i<length;i++)
{
sum[i]=sum[i-1]+nums[i];
}
int pos=0;
int flag;
int j=0;
int vis=0;
for(int i=0;i<length;i++)
{
flag=0;
for(j=max(pos,i);j<length;j++)
{
if(sum[j]-sum[i]+nums[i]>=s)
{
vis=1;
ans=min(ans,j-i+1);
flag=1;
pos=j;
break;
}
}
if(flag==1)
{
j=pos;
}
}
if(vis)
{
return ans;
}
return 0;
}
};