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JumpGame.java
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57 lines (41 loc) · 1.33 KB
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package java_exercise;
public class JumpGame {
/*
* Given an array of non-negative integers, you are initially positioned at the first index of the array.
* Each element in the array represents your maximum jump length at that position.
* Determine if you are able to reach the last index.
* For example:
* A = [2,3,1,1,4], return true.
* A = [3,2,1,0,4], return false.
*/
//recursion version
public boolean canJumpRer(int[] nums) {
return jumpHelper(nums, 0);
}
public boolean jumpHelper(int[] nums, int index) {
if(index == nums.length-1) return true;
if(nums[index] == 0) return false;
for (int i = 1; i <= nums[index]; i++) {
if(jumpHelper(nums, index+i)) {
return true;
}
}
return false;
}
// iteration version
// the situation that the end of the array cannot be reached: max<=i && nums[i] == 0;
// reference: http://www.programcreek.com/2014/03/leetcode-jump-game-java/
public boolean canJumpItr(int[] nums) {
if(nums == null || nums.length <= 1) return true;
//max stands for the largest index that can be reached so far.
int max = nums[0];
for (int i = 0; i < nums.length; i++) {
if(max <= i && nums[i] == 0) return false;
if((i+nums[i]) > max) {
max = i+nums[i];
}
if(max >= (nums.length-1)) return true;
}
return false;
}
}