05 August 2008
一维数组正负数碰撞后剩下的，都为正或都为负
Stack
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class Solution {
public int[] asteroidCollision(int[] asteroids) {
Stack<Integer> s = new Stack<>();
int p = 0;
while (p < asteroids.length) {
if (s.empty() || s.peek() < 0 || asteroids[p] > 0) {
s.push(asteroids[p]);
} else if (s.peek() <= -asteroids[p]) {
if (s.pop() < -asteroids[p]) {
continue;
}
}
p++;
}
int[] ret = new int[s.size()];
for (int i = ret.length - 1; i >= 0; i--) {
ret[i] = s.pop();
}
return ret;
}
}
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class Solution {
public int[] asteroidCollision(int[] asteroids) {
if(asteroids == null || asteroids.length == 1){
return new int[]{};
}
Deque<Integer> stack = new LinkedList<>();
for(int a : asteroids){
if(a > 0){ //feel free to push!
stack.offerFirst(a);
}else{
while(!stack.isEmpty() && stack.peek() > 0 && -a > stack.peekFirst()){
stack.pollFirst();
}
//when we leave while loop, we have three cases:
//1. the stack is empty
if(stack.isEmpty()){
stack.offerFirst(a);
}else{
//2.1 stack.peekFiest is also negative
if(stack.peekFirst() < 0){
stack.offerFirst(a);
//2.2 stack.peekFirst wins the collision or a trie
}else if(stack.peekFirst() == -a){
stack.pollFirst();
}
}
}
}
int[] res = new int[stack.size()];
for(int i = res.length - 1; i >= 0; i--){
res[i] = stack.pollFirst();
}
return res;
}
}