add 787

Author: ca110us

cheapest-flights-within-k-stops.go

@@ -0,0 +1,72 @@
+package main
+
+import (
+	"fmt"
+	"math"
+)
+
+// 787 https://leetcode-cn.com/problems/cheapest-flights-within-k-stops/
+// 动态规划
+func findCheapestPrice(n int, flights [][]int, src int, dst int, K int) int {
+	if n < 1 {
+		return -1
+	}
+	matrix := make([][]int, n)
+	save := make([][]int, n)
+	for i := 0; i < n; i++ {
+		matrix[i] = make([]int, n)
+		save[i] = make([]int, K+1)
+	}
+
+	for i := 0; i < len(flights); i++ {
+		s, e, v := flights[i][0], flights[i][1], flights[i][2]
+		matrix[s][e] = v
+	}
+
+	res := math.MaxInt32
+	queue := make([]int, 0, 2*n)
+	queue = append(queue, src)
+	step := 0
+
+	for len(queue) > 0 && step <= K {
+
+		preLen := len(queue)
+		if preLen > n {
+			fmt.Println(len(queue))
+		}
+		// fmt.Println("start ", s, "  ", queue)
+		for j := 0; j < preLen; j++ {
+			s := queue[0]
+			queue = queue[1:]
+			for i := 0; i < n; i++ {
+				if matrix[s][i] <= 0 {
+					continue
+				}
+				if step == 0 {
+					save[i][step] = 0 + matrix[s][i]
+				} else {
+					s := save[s][step-1] + matrix[s][i]
+					if s < save[i][step] || save[i][step] == 0 {
+						save[i][step] = s
+					} else {
+						continue
+					}
+				}
+				if save[i][step] > res {
+					continue
+				}
+
+				if i == dst {
+					res = save[i][step]
+				}
+				queue = append(queue, i)
+			}
+		}
+		step++
+	}
+
+	if res == math.MaxInt32 {
+		return -1
+	}
+	return res
+}