LeetCode第五天

leetcode 第五天

2018年1月6日

22.(566) Reshape the Matrix

JAVA

class Solution {public int[][] matrixReshape(int[][] nums, int r, int c) {int[][] newNums = new int[r][c];int size = nums.length*nums[0].length;if(r*c != size)return nums;for(int i=0;i<size;i++){newNums[i/c][i%c] = nums[i/nums[0].length][i%nums[0].length];}return newNums;}
}

23.(268) Missing Number

JAVA

class Solution {/*数列求和思想*/public int missingNumber(int[] nums) {int expectSum = nums.length*(nums.length+1)/2;int actualSum = 0;for(int num : nums) actualSum += num;return expectSum - actualSum;}
}

24.(243) ==Shortest Word Distance==

JAVA

class Solution {public int shortestDistance(String[] words,String word1,String word2) {int idx1 = -1,idx2 = -1;int minDistance = words.length;int currentDistance;for(int i =0;i<words.length;i++){if(words[i].equals(word1))idx1=i;else if(words[i].equals(word2))idx2=i;if(idx1 != -1 && idx2 != -1){minDistance = Math.min(minDistance,Math.abs(idx1-idx2));}}return minDistance;}
}

25.(561) Array Partition I

JAVA

class Solution {public int arrayPairSum(int[] nums) {Arrays.sort(nums);int minSum = 0;for(int i = 0;i<nums.length;i+=2){minSum += Math.min(nums[i],nums[i+1]);}return minSum;}
}

26.(746) ==Min Cost Climbing Stairs==

==新知识点：动态规划（有点难度）==

JAVA

class Solution {public int minCostClimbingStairs(int[] cost) {int f1=0;int f2=0;int f3=0;//f3为到达每一个楼层所需要花费的最小钱数(此楼层花费不算)for(int i = 2;i <= cost.length;i++){f3 = Math.min(f1+cost[i-2],f2+cost[i-1]);f1 = f2;f2 = f3;}return f3;}
}

27.(724) Find Pivot Index

JAVA

class Solution {public int pivotIndex(int[] nums) {int sum = 0,leftSum = 0;for(int num : nums) sum+=num;for(int i = 0;i < nums.length;i++){if(leftSum == sum - leftSum - nums[i])return i;leftSum += nums[i];}return -1;}
}

28.(66) Plus One

JAVA

class Solution {public int[] plusOne(int[] digits) {int n = digits.length;for(int i = n-1;i>=0;i--){if(digits[i]<9){digits[i]++;return digits;}digits[i] = 0;}//此处是为了防止原始数字为999...的情况int[] result = new int[n+1];result[0] = 1;return result;}
}

29.(1) Two Sum

==注意Map/HashMap的声明、get()/containsKey()/put()等操作==

JAVA

class Solution {public int[] twoSum(int[] nums, int target) {Map<Integer,Integer> map = new HashMap<Integer,Integer>();int[] result;for(int i = 0;i<nums.length;i++){if(map.containsKey(target - nums[i])){return new int[] {map.get(target-nums[i]),i};}else{map.put(nums[i],i);}}return null;}
}