LeetCode刷题 Day31
455. Assign Cookies
Assume you are an awesome parent and want to give your children some cookies. But, you should give each child at most one cookie.
Each child i has a greed factor g[i], which is the minimum size of a cookie that the child will be content with; and each cookie j has a size s[j]. If s[j] >= g[i], we can assign the cookie j to the child i, and the child i will be content. Your goal is to maximize the number of your content children and output the maximum number.
Example 1:
Input: g = [1,2,3], s = [1,1]
Output: 1
Explanation: You have 3 children and 2 cookies. The greed factors of 3 children are 1, 2, 3.
And even though you have 2 cookies, since their size is both 1, you could only make the child whose greed factor is 1 content.
You need to output 1.
Example 2:
Input: g = [1,2], s = [1,2,3]
Output: 2
Explanation: You have 2 children and 3 cookies. The greed factors of 2 children are 1, 2.
You have 3 cookies and their sizes are big enough to gratify all of the children,
You need to output 2.
思路:
- 首先排序 greed factor和 cookie 数组
- 用快慢指针方法追踪
代码:
var findContentChildren = function(g, s) {
g.sort((a, b) => a - b);
s.sort((a, b) => a - b);
let gIndex = 0;
let sIndex = 0;
while (sIndex < s.length && gIndex < g.length) {
if (s[sIndex] < g[gIndex]) sIndex++;
else {
sIndex++;
gIndex++;
}
}
return gIndex;
};
时间复杂度: O(nlogn) 空间复杂度: O(1)
376. Wiggle Subsequence
A wiggle sequence is a sequence where the differences between successive numbers strictly alternate between positive and negative. The first difference (if one exists) may be either positive or negative. A sequence with one element and a sequence with two non-equal elements are trivially wiggle sequences.
- For example,
[1, 7, 4, 9, 2, 5]is a wiggle sequence because the differences(6, -3, 5, -7, 3)alternate between positive and negative. - In contrast,
[1, 4, 7, 2, 5]and[1, 7, 4, 5, 5]are not wiggle sequences. The first is not because its first two differences are positive, and the second is not because its last difference is zero.
A subsequence is obtained by deleting some elements (possibly zero) from the original sequence, leaving the remaining elements in their original order.
Given an integer array nums, return the length of the longest wiggle subsequence of nums.
Example 1:
Input: nums = [1,7,4,9,2,5]
Output: 6
Explanation: The entire sequence is a wiggle sequence with differences (6, -3, 5, -7, 3).
Example 2:
Input: nums = [1,17,5,10,13,15,10,5,16,8]
Output: 7
Explanation: There are several subsequences that achieve this length.
One is [1, 17, 10, 13, 10, 16, 8] with differences (16, -7, 3, -3, 6, -8).
Example 3:
Input: nums = [1,2,3,4,5,6,7,8,9]
Output: 2
思路:
- 统计顶点
代码:
var wiggleMaxLength = function(nums) {
let currDiff = 0;
let prevDiff = 0;
let res = 1;
for (let i = 1; i < nums.length; i++) {
currDiff = nums[i] - nums[i - 1];
if (currDiff > 0 && prevDiff <= 0 || currDiff < 0 && prevDiff >= 0) {
res++;
prevDiff = currDiff;
}
}
return res;
};
时间复杂度: O(n) 空间复杂度: O(1)
53. Maximum Subarray
Given an integer array nums, find the
subarray which has the largest sum and return its sum.
Example 1:
Input: nums = [-2,1,-3,4,-1,2,1,-5,4]
Output: 6
Explanation: [4,-1,2,1] has the largest sum = 6.
Example 2:
Input: nums = [1]
Output: 1
Example 3:
Input: nums = [5,4,-1,7,8]
Output: 23
思路:
- 设定一个currSum值，当其为负值的时候 如果再去加后面的nums[i]就是起到了副作用，这个时候应该让其至少为0.
代码:
var maxSubArray = function(nums) {
let res = Number.NEGATIVE_INFINITY;
let currSum = 0;
for (let i = 0; i < nums.length; i++) {
currSum += nums[i];
res = Math.max(res, currSum);
currSum = currSum > 0 ? currSum : 0;
}
return res;
};
时间复杂度: O(n) 空间复杂度: O(1)
