LeetCode – Refresh – Best Time to Buy and Sell Stock iii

III is a kind of I. But it require 2 maximum value. So scan from begin and scan from end to record the maximum value for currrent index.

Then scan the maximum array to obtain the global maximum.

class Solution {
public:
    int maxProfit(vector<int> &prices) {
        if (prices.size() < 2) return 0;
        int len = prices.size(), rec = prices[0], result = 0;
        vector<int> left(len, 0), right(len, 0);
        for (int i = 1; i < len; i++) {
            left[i] = max(left[i-1], prices[i] - rec);
            rec = min(rec, prices[i]);
        }
        rec = prices[len-1];
        for (int i = len-2; i >= 0; i--) {
            right[i] = max(right[i+1], rec - prices[i]);
            rec = max(prices[i], rec);
        }
        for (int i = 0; i < len; i++) {
            result = max(result, left[i] + right[i]);
        }
        return result;
    }
};