# 12 lines Java solution O(n) time O(1) space

• ``````public int jump(int[] nums) {
int max = 0, next = 0, count = 0;
int len = nums.length;
for (int i = 0; i < len; i++) {
if (i > max) {
max = next; //only when i > max, need to update max
count++; //keep record of the num of jumps
}
next = Math.max(next, i + nums[i]);  //the next farthest possible position
}
return count;
}``````

• Your solution is simple and elegant, and it CAN pass all the test cases. But it assumes that we can jump to the end of the array. (I believe the test cases also assumes this)
Try this input [3, 2, 1, 0, 4]. Your code returns 2. But actually there's no way we can jump to the end..

Below is a solution that can test whether an input can jump to the end, if not, returns -1; reference: http://bangbingsyb.blogspot.com/2014/11/leetcode-jump-game-i-ii.html

``````public int jump_v2(int[] nums){
int curMax = 0, njumps=0, i=0;
while (curMax < nums.length-1){
int lastMax = curMax;
for(; i<=lastMax; i++){
curMax = Math.max(curMax, i+nums[i]);
}
njumps++;
if(lastMax == curMax) return -1;
}
return njumps;
}
``````

• just need to change the last line of code:

return max>=len-1?count:-1;

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