代码随想录二刷day34

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前言

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一、力扣1005. K 次取反后最大化的数组和

class Solution {
    public int largestSumAfterKNegations(int[] nums, int K) {
    	// 将数组按照绝对值大小从大到小排序，注意要按照绝对值的大小
	nums = IntStream.of(nums)
		     .boxed()
		     .sorted((o1, o2) -> Math.abs(o2) - Math.abs(o1))
		     .mapToInt(Integer::intValue).toArray();
	int len = nums.length;	    
	for (int i = 0; i < len; i++) {
	    //从前向后遍历，遇到负数将其变为正数，同时K--
	    if (nums[i] < 0 && K > 0) {
	    	nums[i] = -nums[i];
	    	K--;
	    }
	}
	// 如果K还大于0，那么反复转变数值最小的元素，将K用完

	if (K % 2 == 1) nums[len - 1] = -nums[len - 1];
	return Arrays.stream(nums).sum();

    }
}

二、力扣134. 加油站

class Solution {
    public int canCompleteCircuit(int[] gas, int[] cost) {
        int curSum = 0, countSum = 0, index = 0;
        for(int i = 0; i < gas.length; i ++){
            int rest = gas[i] - cost[i];
            countSum += rest;
            curSum += rest;
            if(curSum < 0){
                index = i+1;
                curSum = 0;
            }
        }
        if(countSum < 0)return -1;
        return index;
    }
}

三、力扣135. 分发糖果

class Solution {
    public int candy(int[] ratings) {
        int[] arr = new int[ratings.length];
        Arrays.fill(arr,1);
        for(int i = 1; i < ratings.length; i ++){
            arr[i] = ratings[i] > ratings[i-1] ? arr[i-1]+1:arr[i];
        }
        for(int i = ratings.length-2; i >= 0; i --){
            if(ratings[i] > ratings[i+1]){
                arr[i] = Math.max(arr[i], arr[i+1]+1);
            }
        }
        int res = 0;
        for(int a : arr){
            res += a;
        }
        return res;
    }
}