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Commit 5e1a4b4

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implement: 55
1 parent 6934f92 commit 5e1a4b4

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‎src/jump-game/res.js‎

Lines changed: 81 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -4,6 +4,11 @@
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* @param {number[]} nums
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* @return {boolean}
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*/
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/**
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* 贪心:从右向左迭代,对于每个节点我们检查是否存在一步跳跃可以到达 GOOD 的位置(currPosition + nums[currPosition] >= leftmostGoodIndex)。如果可以到达,当前位置也标记为 GOOD ,同时,这个位置将成为新的最左边的 GOOD 位置,一直重复到数组的开头,如果第一个坐标标记为 GOOD 意味着可以从第一个位置跳到最后的位置。
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* @param {*} nums
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*/
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var canJump = function(nums) {
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let lastPos = nums.length - 1;
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for (let index = nums.length - 1; index >= 0; index--) {
@@ -14,4 +19,79 @@ var canJump = function(nums) {
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}
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return lastPos === 0;
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};
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};
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/**
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* 回溯法:从第一个位置开始,模拟所有可以跳到的位置,然后从当前位置重复上述操作,当没有办法继续跳的时候,就回溯。
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* @param {*} nums
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*/
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const canJump = (nums) => {
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const jumpAnalysis = (index) => {
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if (index === nums.length-1) return true;
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const maxLen = Math.min(index + nums[index], nums.length-1);
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for (let i = index + 1; i <= maxLen; i++) {
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if (jumpAnalysis(i)) return true;
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}
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return false;
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}
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return jumpAnalysis(0);
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}
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/**
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* 动态规划:自顶向下
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* @param {*} nums
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*/
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const canJump = (nums) => {
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const mem = nums.map(() => -1);
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mem[nums.length - 1] = 1;
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const jumpAnalysis = (index) => {
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// 当前元素位置如果已经计算过则返回结果
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if (mem[index] !== -1) {
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return mem[index] === 1 ? true : false;
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}
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// 未计算的位置根据可走步数更新 mem
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const maxLen = Math.min(index + nums[index], nums.length-1);
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for (let i = index + 1; i <= maxLen; i++) {
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// 如果当前位置已可以跳到结果那么提前结束返回结果
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if (jumpAnalysis(i)) {
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mem[i] = 1;
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return true;
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}
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}
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// 标定当前位置无用
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mem[index] = 0;
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return false;
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}
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return jumpAnalysis(0);
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}
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/**
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* 动态规划:自底向上
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* @param {*} nums
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*/
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const canJump = (nums) => {
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const len = nums.length;
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if (!len) return false;
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if (len === 1) return true;
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const mem = nums.map(() => 0);
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mem[nums.length - 1] = 1;
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for (let i = nums.length - 2; i >= 0; i--) {
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const maxLen = Math.min(i + nums[i], nums.length-1);
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for (let j = i+1; j <= maxLen; j++) {
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if (mem[j]) {
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mem[i] = 1;
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break;
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}
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}
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}
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return mem[0] === 1;
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}
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