leetcode:best time buy and sell stock系列

best time buy and sell stock系列

最近把leetcode上“best time buy and sell stock”系列一共5个问题整理了一下，题目就补贴出来了，在leetcode上面就能找到。

best time buy and sell stock 1

public int maxProfit(int[] prices) {
        if (prices==null || prices.length == 0) {
            return 0;
        }
        int maxProfile = 0;
        int minValue = 1 << 30;
        for(int price:prices) {
            minValue = Math.min(minValue,price);
            maxProfile = Math.max(maxProfile,price-minValue);
        }
        return maxProfile;
    }

best time buy and sell stock2

 public int maxProfit(int[] prices) {
        /*if(prices==null || prices.length==0) {
            return 0;
        }*/
        int sum = 0;
        int diff;
        for(int i=1;i<prices.length;i++){
            diff = prices[i] - prices[i-1];
            if(diff>0) {
                sum+=diff;
            }
        }
        return sum;
    }

best time buy and sell stock3

public int maxProfit(int[] prices) {
        if(prices==null||prices.length==0){
            return 0;
        }
        int[] left = new int[prices.length];
        int[] right = new int[prices.length];
        for(int i=1;i<prices.length;i++){
            left[i] = left[i-1] + Math.max(prices[i]-prices[i-1],0);
        }

        for(int i=prices.length-1;i>0;i--){
            right[i-1] = right[i] + Math.max(prices[i] - prices[i-1],0);
        }

        int max = Integer.MIN_VALUE;
        for(int i=0;i<prices.length;i++){
            if(i<prices.length-1) {
                max = Math.max(left[i] + right[i+1],max);
            } else {
                max = Math.max(max,left[i]);
            }

        }
        return max;
    }

best time buy and sell stock 4

public int maxProfit(int k, int[] prices) {
        if (prices == null || prices.length == 0) {
            return 0;
        }

        if (k>=prices.length/2){
            int sum = 0;
            for(int i=1;i<prices.length;i++){
                sum = Math.max(sum,sum + prices[i]-prices[i-1]);
            }
            return sum;
        }
        int curMax;
        int[] dp = new int[prices.length];
        for(int i=1;i<=k;i++){
            curMax = 0 - prices[0];
            for(int j=1;j<prices.length;j++){
                curMax = Math.max(curMax,dp[j]-prices[j]);
                dp[j] = Math.max(dp[j-1],curMax+prices[j]);
            }
        }
        return dp[prices.length-1];
    }

best time buy and sell stock with cool down

public int maxProfit(int[] prices) {
        if (prices == null || prices.length == 0) {
            return 0;
        }
        int[]buy = new int[prices.length];
        int[]sell = new int[prices.length];
        sell[0] = 0;
        buy[0] = 0-prices[0];
        int maxProfile = 0;
        for(int i=1;i<prices.length;i++){
            if(i>1){
                buy[i] = Math.max(buy[i-1]+prices[i-1]-prices[i],sell[i-2]-prices[i]);
            }else{
                buy[i] = buy[i-1]+prices[i-1]-prices[i];
            }
            sell[i] = Math.max(sell[i-1]-prices[i-1]+prices[i],buy[i-1] + prices[i]);
            maxProfile = Math.max(maxProfile,sell[i]);
        }
        return maxProfile;
    }