int maxProfit(vector<int> &prices) {
int len = prices.size();
if(!len) return 0;
vector<int> profitLeft(len, 0);
vector<int> profitRight(len, 0);
int maxp = 0, low = prices[0], high = prices[len-1];
for(int i=1; i<len; ++i) {
if(prices[i] < low) low = prices[i];
profitLeft[i] = max(profitLeft[i-1], prices[i]-low);
}
for(int i=len-2; i>=0; --i) {
if(prices[i] > high) high = prices[i];
profitRight[i] = max(profitRight[i+1], high-prices[i]);
maxp = max(maxp, profitLeft[i]+profitRight[i]);
}
return maxp;
}
int maxProfit(vector<int>& prices) {
int n = prices.size();
if(n < 2) return 0;
vector<int> minValLeft(n, 0);
vector<int> maxValLeft(n, 0);
vector<int> minValRight(n, 0);
vector<int> maxValRight(n, 0);
vector<int> profitLeft(n, 0);
vector<int> profitRight(n, 0);
minValLeft[0] = prices[0];
maxValLeft[0] = prices[0];
minValRight[n - 1] = prices[n - 1];
maxValRight[n - 1] = prices[n - 1];
profitLeft[0] = 0;
profitRight[n - 1] = 0;
for(int i = 1; i < n; i++) {
minValLeft[i] = min(minValLeft[i - 1], prices[i]);
maxValLeft[i] = max(maxValLeft[i - 1], prices[i]);
profitLeft[i] = max(profitLeft[i - 1], prices[i] - minValLeft[i - 1]);
}
for(int i = n - 2; i >= 0; i--) {
minValRight[i] = min(minValRight[i + 1], prices[i]);
maxValRight[i] = max(maxValRight[i + 1], prices[i]);
profitRight[i] = max(profitRight[i + 1], maxValRight[i + 1] - prices[i]);
}
int res = 0;
for(int i = 0; i < n - 1; i++) {
res = max(res, maxValRight[i + 1] - minValLeft[i]);
}
for(int i = 0; i < n - 1; i++) {
res = max(res, profitLeft[i] + profitRight[i + 1]);
}
return res;
}