代码随想录算法训练营第32天｜122. 买卖股票的最佳时机 II，55. 跳跃游戏，45. 跳跃游戏 II

Day 32

122. 买卖股票的最佳时机 II

class Solution {
public:
    int maxProfit(vector& prices) {   
        int ans = 0;
        int n = prices.size();
        for (int i = 1; i < n; ++i) {
            ans += max(0, prices[i] - prices[i - 1]);
        }
        return ans;
    }
};

java版：

class Solution {
    public int maxProfit(int[] prices) {
        int ans = 0;
        int n = prices.length;
        for (int i = 1; i < n; ++i) {
            ans += Math.max(0, prices[i] - prices[i - 1]);
        }
        return ans;
    }
}

55. 跳跃游戏

class Solution {
public:
    bool canJump(vector& nums) {
        int k = 0;
        for (int i = 0; i < nums.size(); i++) {
            if (i > k) return false;
            k = max(k, i + nums[i]);
        }
        return true;
    }
};

java版：

public class Solution {
    public boolean canJump(int[] nums) {
        int n = nums.length;
        int rightmost = 0;
        for (int i = 0; i < n; ++i) {
            if (i <= rightmost) {
                rightmost = Math.max(rightmost, i + nums[i]);
                if (rightmost >= n - 1) {
                    return true;
                }
            }
        }
        return false;
    }
}

45. 跳跃游戏 II

class Solution {
public:
    int jump(vector& nums) {
        int maxPos = 0, n = nums.size(), end = 0, step = 0;
        for (int i = 0; i < n - 1; ++i) {
            if (maxPos >= i) {
                maxPos = max(maxPos, i + nums[i]);
                if (i == end) {
                    end = maxPos;
                    ++step;
                }
            }
        }
        return step;
    }
};

java版：

public int jump(int[] nums) {
    int end = 0;
    int maxPosition = 0; 
    int steps = 0;
    for(int i = 0; i < nums.length - 1; i++){
        //找能跳的最远的
        maxPosition = Math.max(maxPosition, nums[i] + i); 
        if( i == end){ //遇到边界，就更新边界，并且步数加一
            end = maxPosition;
            steps++;
        }
    }
    return steps;
}