diff --git a/problems/0053.最大子序和.md b/problems/0053.最大子序和.md index b5fb7642..d0680a3b 100644 --- a/problems/0053.最大子序和.md +++ b/problems/0053.最大子序和.md @@ -230,6 +230,60 @@ var maxSubArray = function(nums) { }; ``` + +### C: +贪心: +```c +int maxSubArray(int* nums, int numsSize){ + int maxVal = INT_MIN; + int subArrSum = 0; + + int i; + for(i = 0; i < numsSize; ++i) { + subArrSum += nums[i]; + // 若当前局部和大于之前的最大结果,对结果进行更新 + maxVal = subArrSum > maxVal ? subArrSum : maxVal; + // 若当前局部和为负,对结果无益。则从nums[i+1]开始应重新计算。 + subArrSum = subArrSum < 0 ? 0 : subArrSum; + } + + return maxVal; +} +``` + +动态规划: +```c +/** + * 解题思路:动态规划: + * 1. dp数组:dp[i]表示从0到i的子序列中最大序列和的值 + * 2. 递推公式:dp[i] = max(dp[i-1] + nums[i], nums[i]) + 若dp[i-1]<0,对最后结果无益。dp[i]则为nums[i]。 + * 3. dp数组初始化:dp[0]的最大子数组和为nums[0] + * 4. 推导顺序:从前往后遍历 + */ + +#define max(a, b) (((a) > (b)) ? (a) : (b)) + +int maxSubArray(int* nums, int numsSize){ + int dp[numsSize]; + // dp[0]最大子数组和为nums[0] + dp[0] = nums[0]; + // 若numsSize为1,应直接返回nums[0] + int subArrSum = nums[0]; + + int i; + for(i = 1; i < numsSize; ++i) { + dp[i] = max(dp[i - 1] + nums[i], nums[i]); + + // 若dp[i]大于之前记录的最大值,进行更新 + if(dp[i] > subArrSum) + subArrSum = dp[i]; + } + + return subArrSum; +} +``` + ### TypeScript **贪心** @@ -267,5 +321,6 @@ function maxSubArray(nums: number[]): number { + -----------------------
diff --git a/problems/0055.跳跃游戏.md b/problems/0055.跳跃游戏.md index 94614242..17a3b4f4 100644 --- a/problems/0055.跳跃游戏.md +++ b/problems/0055.跳跃游戏.md @@ -154,6 +154,30 @@ var canJump = function(nums) { }; ``` + +### C +```c +#define max(a, b) (((a) > (b)) ? (a) : (b)) + +bool canJump(int* nums, int numsSize){ + int cover = 0; + + int i; + // 只可能获取cover范围中的步数,所以i<=cover + for(i = 0; i <= cover; ++i) { + // 更新cover为从i出发能到达的最大值/cover的值中较大值 + cover = max(i + nums[i], cover); + + // 若更新后cover可以到达最后的元素,返回true + if(cover >= numsSize - 1) + return true; + } + + return false; +} +``` + + ### TypeScript ```typescript diff --git a/problems/0122.买卖股票的最佳时机II.md b/problems/0122.买卖股票的最佳时机II.md index 78aa5952..1e7b77d8 100644 --- a/problems/0122.买卖股票的最佳时机II.md +++ b/problems/0122.买卖股票的最佳时机II.md @@ -281,7 +281,7 @@ function maxProfit(prices: number[]): number { ``` C: - +贪心: ```c int maxProfit(int* prices, int pricesSize){ int result = 0; @@ -296,5 +296,27 @@ int maxProfit(int* prices, int pricesSize){ } ``` +动态规划: +```c +#define max(a, b) (((a) > (b)) ? (a) : (b)) + +int maxProfit(int* prices, int pricesSize){ + int dp[pricesSize][2]; + dp[0][0] = 0 - prices[0]; + dp[0][1] = 0; + + int i; + for(i = 1; i < pricesSize; ++i) { + // dp[i][0]为i-1天持股的钱数/在第i天用i-1天的钱买入的最大值。 + // 若i-1天持股,且第i天买入股票比i-1天持股时更亏,说明应在i-1天时持股 + dp[i][0] = max(dp[i-1][0], dp[i-1][1] - prices[i]); + //dp[i][1]为i-1天不持股钱数/在第i天卖出所持股票dp[i-1][0] + prices[i]的最大值 + dp[i][1] = max(dp[i-1][1], dp[i-1][0] + prices[i]); + } + // 返回在最后一天不持股时的钱数(将股票卖出后钱最大化) + return dp[pricesSize - 1][1]; +} +``` + -----------------------
diff --git a/problems/0135.分发糖果.md b/problems/0135.分发糖果.md index b8bdae0e..72f3dd56 100644 --- a/problems/0135.分发糖果.md +++ b/problems/0135.分发糖果.md @@ -238,6 +238,49 @@ var candy = function(ratings) { }; ``` + +### C +```c +#define max(a, b) (((a) > (b)) ? (a) : (b)) + +int *initCandyArr(int size) { + int *candyArr = (int*)malloc(sizeof(int) * size); + + int i; + for(i = 0; i < size; ++i) + candyArr[i] = 1; + + return candyArr; +} + +int candy(int* ratings, int ratingsSize){ + // 初始化数组,每个小孩开始至少有一颗糖 + int *candyArr = initCandyArr(ratingsSize); + + int i; + // 先判断右边是否比左边评分高。若是,右边孩子的糖果为左边孩子+1(candyArr[i] = candyArr[i - 1] + 1) + for(i = 1; i < ratingsSize; ++i) { + if(ratings[i] > ratings[i - 1]) + candyArr[i] = candyArr[i - 1] + 1; + } + + // 再判断左边评分是否比右边高。 + // 若是,左边孩子糖果为右边孩子糖果+1/自己所持糖果最大值。(若糖果已经比右孩子+1多,则不需要更多糖果) + // 举例:ratings为[1, 2, 3, 1]。此时评分为3的孩子在判断右边比左边大后为3,虽然它比最末尾的1(ratings[3])大,但是candyArr[3]为1。所以不必更新candyArr[2] + for(i = ratingsSize - 2; i >= 0; --i) { + if(ratings[i] > ratings[i + 1]) + candyArr[i] = max(candyArr[i], candyArr[i + 1] + 1); + } + + // 求出糖果之和 + int result = 0; + for(i = 0; i < ratingsSize; ++i) { + result += candyArr[i]; + } + return result; +} +``` + ### TypeScript ```typescript @@ -264,6 +307,5 @@ function candy(ratings: number[]): number { - -----------------------
diff --git a/problems/0376.摆动序列.md b/problems/0376.摆动序列.md index acd8996e..6822896e 100644 --- a/problems/0376.摆动序列.md +++ b/problems/0376.摆动序列.md @@ -298,6 +298,35 @@ var wiggleMaxLength = function(nums) { }; ``` + +### C +**贪心** +```c +int wiggleMaxLength(int* nums, int numsSize){ + if(numsSize <= 1) + return numsSize; + + int length = 1; + int preDiff , curDiff; + preDiff = curDiff = 0; + for(int i = 0; i < numsSize - 1; ++i) { + // 计算当前i元素与i+1元素差值 + curDiff = nums[i+1] - nums[i]; + + // 若preDiff与curDiff符号不符,则子序列长度+1。更新preDiff的符号 + // 若preDiff与curDiff符号一致,当前i元素为连续升序/连续降序子序列的中间元素。不被记录入长度 + // 注:当preDiff为0时,curDiff为正或为负都属于符号不同 + if((curDiff > 0 && preDiff <= 0) || (preDiff >= 0 && curDiff < 0)) { + preDiff = curDiff; + length++; + } + } + + return length; +} +``` + + ### TypeScript **贪心** diff --git a/problems/1005.K次取反后最大化的数组和.md b/problems/1005.K次取反后最大化的数组和.md index 80c47147..79767deb 100644 --- a/problems/1005.K次取反后最大化的数组和.md +++ b/problems/1005.K次取反后最大化的数组和.md @@ -211,6 +211,46 @@ var largestSumAfterKNegations = function(nums, k) { }; ``` + +### C +```c +#define abs(a) (((a) > 0) ? (a) : (-(a))) + +// 对数组求和 +int sum(int *nums, int numsSize) { + int sum = 0; + + int i; + for(i = 0; i < numsSize; ++i) { + sum += nums[i]; + } + return sum; +} + +int cmp(const void* v1, const void* v2) { + return abs(*(int*)v2) - abs(*(int*)v1); +} + +int largestSumAfterKNegations(int* nums, int numsSize, int k){ + qsort(nums, numsSize, sizeof(int), cmp); + + int i; + for(i = 0; i < numsSize; ++i) { + // 遍历数组,若当前元素<0则将当前元素转变,k-- + if(nums[i] < 0 && k > 0) { + nums[i] *= -1; + --k; + } + } + + // 若遍历完数组后k还有剩余(此时所有元素应均为正),则将绝对值最小的元素nums[numsSize - 1]变为负 + if(k % 2 == 1) + nums[numsSize - 1] *= -1; + + return sum(nums, numsSize); +} +``` + ### TypeScript ```typescript @@ -235,5 +275,6 @@ function largestSumAfterKNegations(nums: number[], k: number): number { + -----------------------