day32打卡

5. 买卖股票的最佳时机II

var maxProfit = function(prices) {
    const n = prices.length;
    const dp = new Array(n).fill(0).map(v => new Array(2).fill(0));
    dp[0][0] = 0, dp[0][1] = -prices[0];
    for (let i = 1; i < n; ++i) {
        dp[i][0] = Math.max(dp[i - 1][0], dp[i - 1][1] + prices[i]);
        dp[i][1] = Math.max(dp[i - 1][1], dp[i - 1][0] - prices[i]);
    }
    return dp[n - 1][0];
};

6. 跳跃游戏

var canJump = function(nums) {
    // 必须到达end下标的数字
    let end = nums.length - 1;

    for (let i = nums.length - 2; i >= 0; i--) {
        if (end - i <= nums[i]) {
            end = i;
        }
    }

    return end == 0;
};

7. 跳跃游戏II

var jump = function(nums) {
    let curIndex = 0
    let nextIndex = 0
    let steps = 0
    for(let i = 0; i < nums.length - 1; i++) {
        nextIndex = Math.max(nums[i] + i, nextIndex)
        if(i === curIndex) {
            curIndex = nextIndex
            steps++
        }
    }

    return steps
};