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lintcode151.cpp
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lintcode151.cpp
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class Solution {
public:
/**
* @param prices: Given an integer array
* @return: Maximum profit
*/
int maxProfit(vector<int> &prices) {
int n = prices.size();
if(n <= 1)
return 0;
/**
* dp[i][k][0/1]: 在第i天進行第k次交易的最大獲益
* 0 <= i < n
* k = 0(x), 1, 2
*/
vector<vector<vector<int> > > dp(n, vector<vector<int>>(3, vector<int>(2)));
// base case on 0-th day
for(int k = 0; k <=2; ++k) {
dp[0][k][0] = 0;
dp[0][k][1] = -prices[0];
}
// base case on k = 0
for(int i = 0; i < n; ++i) {
dp[i][0][0] = 0;
dp[i][0][1] = INT_MIN;
}
for(int i = 1; i < n; ++i) {
for(int k = 1; k <= 2; ++k) {
// no stock
dp[i][k][0] = max(dp[i - 1][k][0], dp[i - 1][k][1] + prices[i]);
// hold stock
dp[i][k][1] = max(dp[i - 1][k][1], dp[i - 1][k - 1][0] - prices[i]);
}
}
return dp[n - 1][2][0];
}
};
class Solution {
public:
/**
* @param prices: Given an integer array
* @return: Maximum profit
*/
int maxProfit(vector<int> &prices) {
// write your code here
int n = prices.size();
if(n == 0)
return 0;
int buy1 = INT_MIN, buy2 = INT_MIN;
int sell1 = 0, sell2 = 0;
for(int price : prices) {
buy1 = max(buy1, -price);
sell1 = max(sell1, buy1 + price);
buy2 = max(buy2, sell1 - price);
sell2 = max(sell2, buy2 + price);
}
return sell2;
}
};