Best Time to Buy and Sell Stock I, II, III

这几道题最好连着做, 模式就是loc 和global比，难点在于求出loc，咦，我做过这个梦吔

I 只能交易一次，那么loc就和0比 loc = max(loc+diff, 0)

为啥是loc+当天diff呢？比如 1,2,4， 1买进，2-1的差价在loc里存着，到了4 的时候4和1 的差价=4-2 + 2-1 = loc + p[i]-p[i-1]

public class Solution {
    public int maxProfit(List<Integer> prices) {
        if(prices==null||prices.size()==0) return 0;
        int len =prices.size(), loc=0, global = 0;
        for(int i=1;i<len;i++){ 
                loc = Math.max(prices.get(i)-prices.get(i-1)+loc,0);// +loc 的意思是如果之前没卖掉，那么现在卖掉的获利
                global = Math.max(loc,global);
        }
        return global;
    }
}
//http://blog.csdn.net/linhuanmars/article/details/23162793

 

II 能无限次交易，那loc就看今天买划算否, loc = Max(loc, loc + diff)

public class Solution {
    public int maxProfit(List<Integer> prices) {
        if(prices==null||prices.size()==0) return 0;
        int len = prices.size();
        int loc=0, global = 0;
        for(int i=1;i<len;i++){
            loc = Math.max(loc+prices.get(i)-prices.get(i-1), loc);
            global = Math.max(loc, global);
        }
        return global;
    }
}

 

III at most two transactions

天题系列哟