121 Best Time to Buy and Sell Stock
Say you have an array for which the ith element is the price of a given stock on day $$i$$.
If you were only permitted to complete at most one transaction (i.e., buy one and sell one share of the stock), design an algorithm to find the maximum profit.
Example 1:
Input: [7, 1, 5, 3, 6, 4]
Output: 5
max. difference = 6-1 = 5 (not 7-1 = 6, as selling price needs to be larger than buying price)
Example 2:
Input: [7, 6, 4, 3, 1]
Output: 0
In this case, no transaction is done, i.e. max profit = 0.
Solution:
class Solution {
public:
int maxProfit(vector<int>& prices) {
int n = prices.size();
if ( n <= 1 ) return 0;
int minP = prices[0], maxP = 0;
for ( int i = 1; i <= n-1; i++ ) {
minP = min(minP, prices[i]);
maxP = max(maxP, prices[i] - minP);
}
return maxP;
}
};