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Commitd013ca2

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greedy jump games 41, 45
1 parent7499c58 commitd013ca2

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5 files changed

+114
-2
lines changed

5 files changed

+114
-2
lines changed

‎Hard/41-firstMissingPositive.js‎

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/**
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* Solution: keep swapping elements until the element is in the right position.
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* e.g. [3,1,2] --> [2,1,3] -> [1,2,3], now 1 is in the right position.
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* special cases: the element is <=0, or is bigger the length of the array or
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* there is a duplicate in the position at nums[i] - 1 stop swapping, otherewise,
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* it will be an infinite loop.
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* if every element is in the right position, then just simpily return the last element + 1
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*
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*@param {number[]} nums
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*@return {number}
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*/
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varfirstMissingPositive=function(nums){
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if(nums.length<=0)return1;
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for(vari=0;i<nums.length;i++){
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while(nums[i]!==i+1){
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if(nums[i]<=0)break;
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if(nums[i]>nums.length-1||nums[nums[i]-1]===nums[i])break;
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swap(nums,nums[i]-1,i);
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}
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}
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for(varj=0;j<nums.length;j++){
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if(nums[j]!==j+1){
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returnj+1;
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}
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}
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// if every element is in the right position, then just simpily return the last element + 1
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returnnums[nums.length-1]+1;
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};
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varswap=function(nums,i,j){
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vartmp=nums[i];
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nums[i]=nums[j];
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nums[j]=tmp;
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};

‎Hard/45-jumpGameII.js‎

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/**
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*@param {number[]} nums
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*@return {number}
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*/
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varjump=function(nums){
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varjumpTo=0;
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varlastReach=0;
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varjumps=0;
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for(vari=0;i<nums.length&&i<=jumpTo;i++){
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//when last jump can not reach i, increase the step by 1
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if(i>lastReach){
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jumps++;
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lastReach=jumpTo;
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}
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jumpTo=Math.max(jumpTo,nums[i]+i);
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}
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returnlastReach>=nums.length-1 ?jumps :0;
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};
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// second solution, easy understanding. Nice solution. BFS
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// [2,3,1,1,4] 2 -> 3, 1 -> 4
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varjump=function(nums){
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varcurr=0;
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varnext=0;
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varjumps=0;
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varlength=nums.length;
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for(vari=0;i<length;){
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if(curr>=length-1)break;
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// find the next (max jump to) of every element before (including) current element
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// once the next is chosen, it is one step jump.
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while(i<=curr){
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next=Math.max(i+nums[i],next);
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i++;
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}
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jumps++;
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curr=next;
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}
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returnjumps;
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};

‎Hard/57-insertInterval.js‎

Lines changed: 7 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -6,6 +6,11 @@
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* }
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*/
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/**
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* Solutions: 3 scenarios,
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* 1) [[1,2], [5,6]] insert [3,4], push [1,2] (first if),
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* 2) continue step 1, push [3,4] (2nd if), push[5,6] (2nd if)
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* 3) another example, [[1,3], [3,5]] insert [2,4]
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*
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*@param {Interval[]} intervals
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*@param {Interval} newInterval
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*@return {Interval[]}
@@ -18,7 +23,8 @@ var insert = function(intervals, newInterval) {
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}elseif(intervals[i].start>newInterval.end){
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result.push(newInterval);
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newInterval=intervals[i];
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}elseif(intervals[i].end>=newInterval.start||intervals[i].start<=newInterval.end){
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}else{
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// this case is (intervals[i].end >= newInterval.start || intervals[i].start <= newInterval.end)
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newInterval.start=Math.min(intervals[i].start,newInterval.start);
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newInterval.end=Math.max(intervals[i].end,newInterval.end);
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}

‎Medium/55-jumpGame.js‎

Lines changed: 29 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1,6 +1,6 @@
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/**
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* Key: one scenario return false, is when you meet 0 and the max move can't reach to the end.
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* becaue no moves can be made when the element is 0.
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* becaue no moves can be made when the element is 0.
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*
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*@param {number[]} nums
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*@return {boolean}
@@ -14,3 +14,31 @@ var canJump = function(nums) {
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returntrue;
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};
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// second try, not good
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varcanJump=function(nums){
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if(nums.length===1)returntrue;
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varmaxJump=0;
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for(vari=0;i<nums.length;i++){
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maxJump=Math.max(maxJump,nums[i]+i);
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if(maxJump===i)returnfalse;
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if(maxJump>=nums.length-1)returntrue;
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}
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returnfalse;
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};
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varcanJump=function(nums){
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if(nums.length<1)returntrue;
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varmaxNextJump=nums[0];
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for(vari=1;i<nums.length;i++){
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// jumped one step
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maxNextJump--;
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if(maxNextJump<0)returnfalse;
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// if steps at positin i is larger than maxNextJump, then nums[i] is the next jump steps.
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if(maxNextJump<nums[i])maxNextJump=nums[i];
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}
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returntrue;
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}

‎README.md‎

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*[25. Reverse Nodes in k-Group](https://leetcode.com/problems/reverse-nodes-in-k-group/) -[Solution](./Hard/25-reverseNodesInKGroup.js)
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*[32. Longest Valid Parentheses](https://leetcode.com/problems/longest-valid-parentheses/) -[Solution](./Hard/32-longestValidParentheses.js)
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*[33. Search in Rotated Sorted Array](https://leetcode.com/problems/search-in-rotated-sorted-array/) -[Solution](./Hard/33-searchRotatedSortedArray.js)
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*[41. First Missing Positive](https://leetcode.com/problems/first-missing-positive/) -[Solution](./Hard/41-firstMissingPositive.js)
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*[45. Jump Game II](https://leetcode.com/problems/jump-game-ii/) -[Solution](./Hard/45-jumpGameII.js)
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*[56. Merge Intervals](https://leetcode.com/problems/merge-intervals/) -[Solution](./Hard/56-MergeIntervals.js)
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*[57. Insert Interval](https://leetcode.com/problems/insert-interval/) -[Solution](./Hard/57-insertInterval.js)
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*[123. Best Time to Buy and Sell Stock III](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-iii/) -[Solution](./Hard/123-bestTimeBuySellStockIII.js)

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