[leetcode] Best Time to Buy and Sell Stock III

class Solution {
public:
int maxProfit(vector<int> &prices) {
const int n=prices.size();
if(n<2){
return 0;
}
vector<int> f(n,0);
vector<int> g(n,0);

int valley=prices[0];
int peak=prices[n-1];

for(int i=1;i<n;i++){//波谷
valley=min(valley,prices[i]);
f[i]=max(f[i-1],prices[i]-valley);
}

for(int j=n-2;j>=0;j--){//波峰
peak=max(peak,prices[j]);
g[j]=max(g[j+1],peak-prices[j]);
}
int max_profit=0;
for(int k=0;k<n;k++){
max_profit=max(max_profit,f[k]+g[k]);//dp
}
return max_profit;
}
};